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Assignment operators assign values to JavaScript variables.

Shift Assignment Operators

Bitwise assignment operators, logical assignment operators, the = operator.

The Simple Assignment Operator assigns a value to a variable.

Simple Assignment Examples

The += operator.

The Addition Assignment Operator adds a value to a variable.

Addition Assignment Examples

The -= operator.

The Subtraction Assignment Operator subtracts a value from a variable.

Subtraction Assignment Example

The *= operator.

The Multiplication Assignment Operator multiplies a variable.

Multiplication Assignment Example

The **= operator.

The Exponentiation Assignment Operator raises a variable to the power of the operand.

Exponentiation Assignment Example

The /= operator.

The Division Assignment Operator divides a variable.

Division Assignment Example

The %= operator.

The Remainder Assignment Operator assigns a remainder to a variable.

Remainder Assignment Example

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The <<= Operator

The Left Shift Assignment Operator left shifts a variable.

Left Shift Assignment Example

The >>= operator.

The Right Shift Assignment Operator right shifts a variable (signed).

Right Shift Assignment Example

The >>>= operator.

The Unsigned Right Shift Assignment Operator right shifts a variable (unsigned).

Unsigned Right Shift Assignment Example

The &= operator.

The Bitwise AND Assignment Operator does a bitwise AND operation on two operands and assigns the result to the the variable.

Bitwise AND Assignment Example

The |= operator.

The Bitwise OR Assignment Operator does a bitwise OR operation on two operands and assigns the result to the variable.

Bitwise OR Assignment Example

The ^= operator.

The Bitwise XOR Assignment Operator does a bitwise XOR operation on two operands and assigns the result to the variable.

Bitwise XOR Assignment Example

The &&= operator.

The Logical AND assignment operator is used between two values.

If the first value is true, the second value is assigned.

Logical AND Assignment Example

The &&= operator is an ES2020 feature .

The ||= Operator

The Logical OR assignment operator is used between two values.

If the first value is false, the second value is assigned.

Logical OR Assignment Example

The ||= operator is an ES2020 feature .

The ??= Operator

The Nullish coalescing assignment operator is used between two values.

If the first value is undefined or null, the second value is assigned.

Nullish Coalescing Assignment Example

The ??= operator is an ES2020 feature .

Test Yourself With Exercises

Use the correct assignment operator that will result in x being 15 (same as x = x + y ).

Start the Exercise

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Home » JavaScript Tutorial » JavaScript Assignment Operators

JavaScript Assignment Operators

Summary : in this tutorial, you will learn how to use JavaScript assignment operators to assign a value to a variable.

Introduction to JavaScript assignment operators

An assignment operator ( = ) assigns a value to a variable. The syntax of the assignment operator is as follows:

In this syntax, JavaScript evaluates the expression b first and assigns the result to the variable a .

The following example declares the counter variable and initializes its value to zero:

The following example increases the counter variable by one and assigns the result to the counter variable:

When evaluating the second statement, JavaScript evaluates the expression on the right-hand first ( counter + 1 ) and assigns the result to the counter variable. After the second assignment, the counter variable is 1 .

To make the code more concise, you can use the += operator like this:

In this syntax, you don’t have to repeat the counter variable twice in the assignment.

The following table illustrates assignment operators that are shorthand for another operator and the assignment:

Chaining JavaScript assignment operators

If you want to assign a single value to multiple variables, you can chain the assignment operators. For example:

In this example, JavaScript evaluates from right to left. Therefore, it does the following:

• Use the assignment operator ( = ) to assign a value to a variable.
• Chain the assignment operators if you want to assign a single value to multiple variables.

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• Assignment operators

An assignment operator assigns a value to its left operand based on the value of its right operand.

The basic assignment operator is equal ( = ), which assigns the value of its right operand to its left operand. That is, x = y assigns the value of y to x . The other assignment operators are usually shorthand for standard operations, as shown in the following definitions and examples.

Simple assignment operator which assigns a value to a variable. The assignment operation evaluates to the assigned value. Chaining the assignment operator is possible in order to assign a single value to multiple variables. See the example.

Addition assignment

The addition assignment operator adds the value of the right operand to a variable and assigns the result to the variable. The types of the two operands determine the behavior of the addition assignment operator. Addition or concatenation is possible. See the addition operator for more details.

Subtraction assignment

The subtraction assignment operator subtracts the value of the right operand from a variable and assigns the result to the variable. See the subtraction operator for more details.

Multiplication assignment

The multiplication assignment operator multiplies a variable by the value of the right operand and assigns the result to the variable. See the multiplication operator for more details.

Division assignment

The division assignment operator divides a variable by the value of the right operand and assigns the result to the variable. See the division operator for more details.

Remainder assignment

The remainder assignment operator divides a variable by the value of the right operand and assigns the remainder to the variable. See the remainder operator for more details.

Exponentiation assignment

This is an experimental technology, part of the ECMAScript 2016 (ES7) proposal. Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future version of browsers as the spec changes.

The exponentiation assignment operator evaluates to the result of raising first operand to the power second operand. See the exponentiation operator for more details.

Left shift assignment

The left shift assignment operator moves the specified amount of bits to the left and assigns the result to the variable. See the left shift operator for more details.

Right shift assignment

The right shift assignment operator moves the specified amount of bits to the right and assigns the result to the variable. See the right shift operator for more details.

Unsigned right shift assignment

The unsigned right shift assignment operator moves the specified amount of bits to the right and assigns the result to the variable. See the unsigned right shift operator for more details.

Bitwise AND assignment

The bitwise AND assignment operator uses the binary representation of both operands, does a bitwise AND operation on them and assigns the result to the variable. See the bitwise AND operator for more details.

Bitwise XOR assignment

The bitwise XOR assignment operator uses the binary representation of both operands, does a bitwise XOR operation on them and assigns the result to the variable. See the bitwise XOR operator for more details.

Bitwise OR assignment

The bitwise OR assignment operator uses the binary representation of both operands, does a bitwise OR operation on them and assigns the result to the variable. See the bitwise OR operator for more details.

Left operand with another assignment operator

In unusual situations, the assignment operator (e.g. x += y ) is not identical to the meaning expression (here x = x + y ). When the left operand of an assignment operator itself contains an assignment operator, the left operand is evaluated only once. For example:

Specifications

Browser compatibility.

• Arithmetic operators

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Assignment Expressions

JavaScript uses the = operator to assign a value to a variable or property. For example:

The = operator expects its left-side operand to be an lvalue: a variable or object property (or array element). It expects its right-side operand to be an arbitrary value of any type. The value of an assignment expression is the value of the right-side operand. As a side effect, the = operator assigns the value on the right to the variable or property on the left so that future references to the variable or property evaluate to the value.

Although assignment expressions are usually quite simple, you may sometimes see the value of an assignment expression used as part of a larger expression. For example, you can assign and test a value in the same expression with code like this:

If you do this, be sure you are clear on the difference between the = and == operators! Note that = has very low precedence and parentheses are usually necessary when the value of an assignment is to be used in a larger expression.

The assignment operator has right-to-left associativity, which means that when multiple assignment operators appear in an expression, they are evaluated from right to left. Thus, you can write code like this to assign a single value to multiple variables:

Assignment with Operation

Besides the normal = assignment operator, JavaScript supports a number of other assignment operators that provide shortcuts by combining assignment with some other operation. For example, the += operator performs addition and assignment. The following expression:

is equivalent to this one:

As you might expect, the += operator works for numbers or strings. For numeric operands, it performs addition and assignment; for string operands, it performs concatenation and assignment.

Similar operators include -= , *= , &= , and so on. Table 4-3 lists them all.

Table 4-3. Assignment operators

In most cases, the expression:

where op is an operator, is equivalent to the expression:

In the first line, the expression a is evaluated once. In the second it is evaluated twice. The two cases will differ only if a includes side effects such as a function call or an increment operator. The following two assignments, for example, are not the same:

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JAVASCRIPT ASSIGNMENT OPERATORS

In this tutorial, you will learn about all the different assignment operators in javascript and how to use them in javascript.

Assignment Operators

In javascript, there are 16 different assignment operators that are used to assign value to the variable. It is shorthand of other operators which is recommended to use.

The assignment operators are used to assign value based on the right operand to its left operand.

The left operand must be a variable while the right operand may be a variable, number, boolean, string, expression, object, or combination of any other.

One of the most basic assignment operators is equal = , which is used to directly assign a value.

Assignment Operators List

Here is the list of all assignment operators in JavaScript:

In the following table if variable a is not defined then assume it to be 10.

Assignment operator

The assignment operator = is the simplest value assigning operator which assigns a given value to a variable.

The assignment operators support chaining, which means you can assign a single value in multiple variables in a single line.

Addition assignment operator

The addition assignment operator += is used to add the value of the right operand to the value of the left operand and assigns the result to the left operand.

On the basis of the data type of variable, the addition assignment operator may add or concatenate the variables.

Subtraction assignment operator

The subtraction assignment operator -= subtracts the value of the right operand from the value of the left operand and assigns the result to the left operand.

If the value can not be subtracted then it results in a NaN .

Multiplication assignment operator

The multiplication assignment operator *= assigns the result to the left operand after multiplying values of the left and right operand.

Division assignment operator

The division assignment operator /= divides the value of the left operand by the value of the right operand and assigns the result to the left operand.

Remainder assignment operator

The remainder assignment operator %= assigns the remainder to the left operand after dividing the value of the left operand by the value of the right operand.

Exponentiation assignment operator

The exponential assignment operator **= assigns the result of exponentiation to the left operand after exponentiating the value of the left operand by the value of the right operand.

Left shift assignment

The left shift assignment operator <<= assigns the result of the left shift to the left operand after shifting the value of the left operand by the value of the right operand.

Right shift assignment

The right shift assignment operator >>= assigns the result of the right shift to the left operand after shifting the value of the left operand by the value of the right operand.

Unsigned right shift assignment

The unsigned right shift assignment operator >>>= assigns the result of the unsigned right shift to the left operand after shifting the value of the left operand by the value of the right operand.

Bitwise AND assignment

The bitwise AND assignment operator &= assigns the result of bitwise AND to the left operand after ANDing the value of the left operand by the value of the right operand.

Bitwise OR assignment

The bitwise OR assignment operator |= assigns the result of bitwise OR to the left operand after ORing the value of left operand by the value of the right operand.

Bitwise XOR assignment

The bitwise XOR assignment operator ^= assigns the result of bitwise XOR to the left operand after XORing the value of the left operand by the value of the right operand.

Logical AND assignment

The logical AND assignment operator &&= assigns value to left operand only when it is truthy .

Note : A truthy value is a value that is considered true when encountered in a boolean context.

Logical OR assignment

The logical OR assignment operator ||= assigns value to left operand only when it is falsy .

Note : A falsy value is a value that is considered false when encountered in a boolean context.

String operators

• Conditional (ternary) operator
• Comma operator

Unary operators

Relational operators.

JavaScript has both binary and unary operators, and one special ternary operator, the conditional operator. A binary operator requires two operands, one before the operator and one after the operator:

For example, 3+4 or x*y .

A unary operator requires a single operand, either before or after the operator:

For example, x++ or ++x .

An assignment operator assigns a value to its left operand based on the value of its right operand. The simple assignment operator is equal ( = ), which assigns the value of its right operand to its left operand. That is, x = y assigns the value of y to x .

There are also compound assignment operators that are shorthand for the operations listed in the following table:

Destructuring

For more complex assignments, the destructuring assignment syntax is a JavaScript expression that makes it possible to extract data from arrays or objects using a syntax that mirrors the construction of array and object literals.

A comparison operator compares its operands and returns a logical value based on whether the comparison is true. The operands can be numerical, string, logical, or object values. Strings are compared based on standard lexicographical ordering, using Unicode values. In most cases, if the two operands are not of the same type, JavaScript attempts to convert them to an appropriate type for the comparison. This behavior generally results in comparing the operands numerically. The sole exceptions to type conversion within comparisons involve the === and !== operators, which perform strict equality and inequality comparisons. These operators do not attempt to convert the operands to compatible types before checking equality. The following table describes the comparison operators in terms of this sample code:

Note:  ( => ) is not an operator, but the notation for Arrow functions .

An arithmetic operator takes numerical values (either literals or variables) as their operands and returns a single numerical value. The standard arithmetic operators are addition ( + ), subtraction ( - ), multiplication ( * ), and division ( / ). These operators work as they do in most other programming languages when used with floating point numbers (in particular, note that division by zero produces Infinity ). For example:

In addition to the standard arithmetic operations (+, -, * /), JavaScript provides the arithmetic operators listed in the following table:

A bitwise operator treats their operands as a set of 32 bits (zeros and ones), rather than as decimal, hexadecimal, or octal numbers. For example, the decimal number nine has a binary representation of 1001. Bitwise operators perform their operations on such binary representations, but they return standard JavaScript numerical values.

The following table summarizes JavaScript's bitwise operators.

Bitwise logical operators

Conceptually, the bitwise logical operators work as follows:

• The operands are converted to thirty-two-bit integers and expressed by a series of bits (zeros and ones). Numbers with more than 32 bits get their most significant bits discarded. For example, the following integer with more than 32 bits will be converted to a 32 bit integer: Before: 11100110111110100000000000000110000000000001 After: 10100000000000000110000000000001
• Each bit in the first operand is paired with the corresponding bit in the second operand: first bit to first bit, second bit to second bit, and so on.
• The operator is applied to each pair of bits, and the result is constructed bitwise.

For example, the binary representation of nine is 1001, and the binary representation of fifteen is 1111. So, when the bitwise operators are applied to these values, the results are as follows:

Note that all 32 bits are inverted using the Bitwise NOT operator, and that values with the most significant (left-most) bit set to 1 represent negative numbers (two's-complement representation). ~x evaluates to the same value that -x - 1 evaluates to.

Bitwise shift operators

The bitwise shift operators take two operands: the first is a quantity to be shifted, and the second specifies the number of bit positions by which the first operand is to be shifted. The direction of the shift operation is controlled by the operator used.

Shift operators convert their operands to thirty-two-bit integers and return a result of the same type as the left operand.

The shift operators are listed in the following table.

Logical operators are typically used with Boolean (logical) values; when they are, they return a Boolean value. However, the && and || operators actually return the value of one of the specified operands, so if these operators are used with non-Boolean values, they may return a non-Boolean value. The logical operators are described in the following table.

Examples of expressions that can be converted to false are those that evaluate to null, 0, NaN, the empty string (""), or undefined.

The following code shows examples of the && (logical AND) operator.

The following code shows examples of the || (logical OR) operator.

The following code shows examples of the ! (logical NOT) operator.

Short-circuit evaluation

As logical expressions are evaluated left to right, they are tested for possible "short-circuit" evaluation using the following rules:

• false && anything is short-circuit evaluated to false.
• true || anything is short-circuit evaluated to true.

The rules of logic guarantee that these evaluations are always correct. Note that the anything part of the above expressions is not evaluated, so any side effects of doing so do not take effect.

In addition to the comparison operators, which can be used on string values, the concatenation operator (+) concatenates two string values together, returning another string that is the union of the two operand strings.

For example,

The shorthand assignment operator += can also be used to concatenate strings.

The conditional operator is the only JavaScript operator that takes three operands. The operator can have one of two values based on a condition. The syntax is:

If condition is true, the operator has the value of val1 . Otherwise it has the value of val2 . You can use the conditional operator anywhere you would use a standard operator.

This statement assigns the value "adult" to the variable status if age is eighteen or more. Otherwise, it assigns the value "minor" to status .

The comma operator ( , ) simply evaluates both of its operands and returns the value of the last operand. This operator is primarily used inside a for loop, to allow multiple variables to be updated each time through the loop.

For example, if a is a 2-dimensional array with 10 elements on a side, the following code uses the comma operator to update two variables at once. The code prints the values of the diagonal elements in the array:

A unary operation is an operation with only one operand.

The delete operator deletes an object, an object's property, or an element at a specified index in an array. The syntax is:

where objectName is the name of an object, property is an existing property, and index is an integer representing the location of an element in an array.

The fourth form is legal only within a with statement, to delete a property from an object.

You can use the delete operator to delete variables declared implicitly but not those declared with the var statement.

If the delete operator succeeds, it sets the property or element to undefined . The delete operator returns true if the operation is possible; it returns false if the operation is not possible.

Deleting array elements

When you delete an array element, the array length is not affected. For example, if you delete a[3] , a[4] is still a[4] and a[3] is undefined.

When the delete operator removes an array element, that element is no longer in the array. In the following example, trees[3] is removed with delete . However, trees[3] is still addressable and returns undefined .

If you want an array element to exist but have an undefined value, use the undefined keyword instead of the delete operator. In the following example, trees[3] is assigned the value undefined , but the array element still exists:

The typeof operator is used in either of the following ways:

The typeof operator returns a string indicating the type of the unevaluated operand. operand is the string, variable, keyword, or object for which the type is to be returned. The parentheses are optional.

Suppose you define the following variables:

The typeof operator returns the following results for these variables:

For the keywords true and null , the typeof operator returns the following results:

For a number or string, the typeof operator returns the following results:

For property values, the typeof operator returns the type of value the property contains:

For methods and functions, the typeof operator returns results as follows:

For predefined objects, the typeof operator returns results as follows:

The void operator is used in either of the following ways:

The void operator specifies an expression to be evaluated without returning a value. expression is a JavaScript expression to evaluate. The parentheses surrounding the expression are optional, but it is good style to use them.

You can use the void operator to specify an expression as a hypertext link. The expression is evaluated but is not loaded in place of the current document.

The following code creates a hypertext link that does nothing when the user clicks it. When the user clicks the link, void(0) evaluates to undefined , which has no effect in JavaScript.

The following code creates a hypertext link that submits a form when the user clicks it.

A relational operator compares its operands and returns a Boolean value based on whether the comparison is true.

The in operator returns true if the specified property is in the specified object. The syntax is:

where propNameOrNumber is a string, numeric, or symbol expression representing a property name or array index, and objectName is the name of an object.

The following examples show some uses of the in operator.

The instanceof operator returns true if the specified object is of the specified object type. The syntax is:

where objectName is the name of the object to compare to objectType , and objectType is an object type, such as Date or Array .

Use instanceof when you need to confirm the type of an object at runtime. For example, when catching exceptions, you can branch to different exception-handling code depending on the type of exception thrown.

For example, the following code uses instanceof to determine whether theDay is a Date object. Because theDay is a Date object, the statements in the if statement execute.

• Operator precedence

The precedence of operators determines the order they are applied when evaluating an expression. You can override operator precedence by using parentheses.

The following table describes the precedence of operators, from highest to lowest.

A more detailed version of this table, complete with links to additional details about each operator, may be found in JavaScript Reference .

• Expressions

An expression is any valid unit of code that resolves to a value.

Every syntactically valid expression resolves to some value but conceptually, there are two types of expressions: with side effects (for example: those that assign value to a variable) and those that in some sense evaluate and therefore resolve to a value.

The expression x = 7 is an example of the first type. This expression uses the = operator to assign the value seven to the variable x . The expression itself evaluates to seven.

The code 3 + 4 is an example of the second expression type. This expression uses the + operator to add three and four together without assigning the result, seven, to a variable. JavaScript has the following expression categories:

• Arithmetic: evaluates to a number, for example 3.14159. (Generally uses arithmetic operators .)
• String: evaluates to a character string, for example, "Fred" or "234". (Generally uses string operators .)
• Logical: evaluates to true or false. (Often involves logical operators .)
• Primary expressions: Basic keywords and general expressions in JavaScript.
• Left-hand-side expressions: Left values are the destination of an assignment.

Primary expressions

Basic keywords and general expressions in JavaScript.

Use the this keyword to refer to the current object. In general, this refers to the calling object in a method. Use this either with the dot or the bracket notation:

Suppose a function called validate validates an object's value property, given the object and the high and low values:

You could call validate in each form element's onChange event handler, using this to pass it the form element, as in the following example:

• Grouping operator

The grouping operator ( ) controls the precedence of evaluation in expressions. For example, you can override multiplication and division first, then addition and subtraction to evaluate addition first.

Left-hand-side expressions

Left values are the destination of an assignment.

You can use the new operator to create an instance of a user-defined object type or of one of the built-in object types. Use new as follows:

The super keyword is used to call functions on an object's parent. It is useful with classes to call the parent constructor, for example.

Spread operator

The spread operator allows an expression to be expanded in places where multiple arguments (for function calls) or multiple elements (for array literals) are expected.

Example: Today if you have an array and want to create a new array with the existing one being part of it, the array literal syntax is no longer sufficient and you have to fall back to imperative code, using a combination of push , splice , concat , etc. With spread syntax this becomes much more succinct:

Similarly, the spread operator works with function calls:

Document Tags and Contributors

• l10n:priority
• JavaScript basics
• JavaScript first steps
• JavaScript building blocks
• Introducing JavaScript objects
• Introduction
• Grammar and types
• Control flow and error handling
• Loops and iteration
• Numbers and dates
• Text formatting
• Regular expressions
• Indexed collections
• Keyed collections
• Working with objects
• Details of the object model
• Using promises
• Iterators and generators
• Meta programming
• Client-side web APIs
• A re-introduction to JavaScript
• JavaScript data structures
• Equality comparisons and sameness
• Inheritance and the prototype chain
• Strict mode
• JavaScript typed arrays
• Memory Management
• Concurrency model and Event Loop
• References:
• ArrayBuffer
• AsyncFunction
• Float32Array
• Float64Array
• GeneratorFunction
• InternalError
• Intl.Collator
• Intl.DateTimeFormat
• Intl.ListFormat
• Intl.NumberFormat
• Intl.PluralRules
• Intl.RelativeTimeFormat
• ReferenceError
• SharedArrayBuffer
• SyntaxError
• Uint16Array
• Uint32Array
• Uint8ClampedArray
• WebAssembly
• decodeURI()
• decodeURIComponent()
• encodeURI()
• encodeURIComponent()
• parseFloat()
• Array comprehensions
• Destructuring assignment
• Expression closures
• Generator comprehensions
• Legacy generator function expression
• Object initializer
• (currently at stage 1) allows the creation of chained function calls in a readable manner. Basically, the pipeline operator provides syntactic sugar on a function call with a single argument allowing you to write">Pipeline operator
• Property accessors
• Spread syntax
• async function expression
• class expression
• delete operator
• function expression
• function* expression
• in operator
• new operator
• void operator
• Legacy generator function
• async function
• for await...of
• for each...in
• function declaration
• import.meta
• try...catch
• Arrow functions
• Default parameters
• Method definitions
• Rest parameters
• The arguments object
• constructor
• element loaded from a different domain for which you violated the same-origin policy.">Error: Permission denied to access property "x"
• InternalError: too much recursion
• RangeError: argument is not a valid code point
• RangeError: invalid array length
• RangeError: invalid date
• RangeError: precision is out of range
• RangeError: radix must be an integer
• RangeError: repeat count must be less than infinity
• RangeError: repeat count must be non-negative
• ReferenceError: "x" is not defined
• ReferenceError: assignment to undeclared variable "x"
• ReferenceError: can't access lexical declaration`X' before initialization
• ReferenceError: deprecated caller or arguments usage
• ReferenceError: invalid assignment left-hand side
• ReferenceError: reference to undefined property "x"
• SyntaxError: "0"-prefixed octal literals and octal escape seq. are deprecated
• SyntaxError: "use strict" not allowed in function with non-simple parameters
• SyntaxError: "x" is a reserved identifier
• SyntaxError: JSON.parse: bad parsing
• SyntaxError: Malformed formal parameter
• SyntaxError: Unexpected token
• SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead
• SyntaxError: a declaration in the head of a for-of loop can't have an initializer
• SyntaxError: applying the 'delete' operator to an unqualified name is deprecated
• SyntaxError: for-in loop head declarations may not have initializers
• SyntaxError: function statement requires a name
• SyntaxError: identifier starts immediately after numeric literal
• SyntaxError: illegal character
• SyntaxError: invalid regular expression flag "x"
• SyntaxError: missing ) after argument list
• SyntaxError: missing ) after condition
• SyntaxError: missing : after property id
• SyntaxError: missing ; before statement
• SyntaxError: missing = in const declaration
• SyntaxError: missing ] after element list
• SyntaxError: missing formal parameter
• SyntaxError: missing name after . operator
• SyntaxError: missing variable name
• SyntaxError: missing } after function body
• SyntaxError: missing } after property list
• SyntaxError: redeclaration of formal parameter "x"
• SyntaxError: return not in function
• SyntaxError: test for equality (==) mistyped as assignment (=)?
• SyntaxError: unterminated string literal
• TypeError: "x" has no properties
• TypeError: "x" is (not) "y"
• TypeError: "x" is not a constructor
• TypeError: "x" is not a function
• TypeError: "x" is not a non-null object
• TypeError: "x" is read-only
• TypeError: 'x' is not iterable
• TypeError: More arguments needed
• TypeError: Reduce of empty array with no initial value
• TypeError: can't access dead object
• TypeError: can't access property "x" of "y"
• TypeError: can't define property "x": "obj" is not extensible
• TypeError: can't delete non-configurable array element
• TypeError: can't redefine non-configurable property "x"
• TypeError: cannot use 'in' operator to search for 'x' in 'y'
• TypeError: cyclic object value
• TypeError: invalid 'instanceof' operand 'x'
• TypeError: invalid Array.prototype.sort argument
• TypeError: invalid arguments
• TypeError: invalid assignment to const "x"
• TypeError: property "x" is non-configurable and can't be deleted
• TypeError: setting getter-only property "x"
• TypeError: variable "x" redeclares argument
• URIError: malformed URI sequence
• Warning: -file- is being assigned a //# sourceMappingURL, but already has one
• Warning: 08/09 is not a legal ECMA-262 octal constant
• Warning: Date.prototype.toLocaleFormat is deprecated
• Warning: JavaScript 1.6's for-each-in loops are deprecated
• Warning: String.x is deprecated; use String.prototype.x instead
• Warning: expression closures are deprecated
• Warning: unreachable code after return statement
• X.prototype.y called on incompatible type
• JavaScript technologies overview
• Lexical grammar
• Enumerability and ownership of properties
• Iteration protocols
• Transitioning to strict mode
• Template literals
• Deprecated features
• ECMAScript 2015 support in Mozilla
• ECMAScript 5 support in Mozilla
• ECMAScript Next support in Mozilla
• Firefox JavaScript changelog
• New in JavaScript 1.1
• New in JavaScript 1.2
• New in JavaScript 1.3
• New in JavaScript 1.4
• New in JavaScript 1.5
• New in JavaScript 1.6
• New in JavaScript 1.7
• New in JavaScript 1.8
• New in JavaScript 1.8.1
• New in JavaScript 1.8.5
• Documentation:
• All pages index
• Methods index
• Properties index
• Pages tagged "JavaScript"
• JavaScript doc status
• The MDN project

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