Revision 984429 of Expressions and operators

<div>{{jsSidebar("Operators")}}</div>

<p>This chapter documents all the JavaScript language operators, expressions and keywords.</p>

<h2 id="Expressions_and_operators_by_category">Expressions and operators by category</h2>

<p>For an alphabetical listing see the sidebar on the left.</p>

<h3 id="Primary_expressions">Primary expressions</h3>

<p>Basic keywords and general expressions in JavaScript.</p>

<dl>
 <dt>{{jsxref("Operators/this", "this")}}</dt>
 <dd>The <code>this</code> keyword refers to the function's execution context.</dd>
 <dt>{{jsxref("Operators/function", "function")}}</dt>
 <dd>The <code>function</code> keyword defines a function expression.</dd>
 <dt>{{jsxref("Operators/class", "class")}}</dt>
 <dd>The <code>class</code> keyword defines a class expression.</dd>
 <dt>{{jsxref("Operators/function*", "function*")}}</dt>
 <dd>The <code>function*</code> keyword defines a generator function expression.</dd>
 <dt>{{jsxref("Operators/yield", "yield")}}</dt>
 <dd>Pause and resume a generator function.</dd>
 <dt>{{jsxref("Operators/yield*", "yield*")}}</dt>
 <dd>Delegate to another generator function or iterable object.</dd>
 <dt>{{jsxref("Global_Objects/Array", "[]")}}</dt>
 <dd>Array initializer/literal syntax.</dd>
 <dt>{{jsxref("Operators/Object_initializer", "{}")}}</dt>
 <dd>Object initializer/literal syntax.</dd>
 <dt>{{jsxref("Global_Objects/RegExp", "/ab+c/i")}}</dt>
 <dd>Regular expression literal syntax.</dd>
 <dt>{{jsxref("Operators/Grouping", "( )")}}</dt>
 <dd>Grouping operator.</dd>
</dl>

<h3 id="Left-hand-side_expressions">Left-hand-side expressions</h3>

<p>Left values are the destination of an assignment.</p>

<dl>
 <dt>{{jsxref("Operators/Property_accessors", "Property accessors", "", 1)}}</dt>
 <dd>Member operators provide access to a property or method of an object<br />
 (<code>object.property</code> and <code>object["property"]</code>).</dd>
 <dt>{{jsxref("Operators/new", "new")}}</dt>
 <dd>The <code>new</code> operator creates an instance of a constructor.</dd>
 <dt><a href="/en-US/docs/Web/JavaScript/Reference/Operators/new.target">new.target</a></dt>
 <dd>In constructors, <code>new.target</code> refers to the constructor that was invoked by {{jsxref("Operators/new", "new")}}.</dd>
 <dt>{{jsxref("Operators/super", "super")}}</dt>
 <dd>The <code>super</code> keyword calls the parent constructor.</dd>
 <dt>{{jsxref("Operators/Spread_operator", "...obj")}}</dt>
 <dd>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.</dd>
</dl>

<h3 id="Increment_and_decrement">Increment and decrement</h3>

<p>Postfix/prefix increment and postfix/prefix decrement operators.</p>

<dl>
 <dt>{{jsxref("Operators/Arithmetic_Operators", "A++", "#Increment")}}</dt>
 <dd>Postfix increment operator.</dd>
 <dt>{{jsxref("Operators/Arithmetic_Operators", "A--", "#Decrement")}}</dt>
 <dd>Postfix decrement operator.</dd>
 <dt>{{jsxref("Operators/Arithmetic_Operators", "++A", "#Increment")}}</dt>
 <dd>Prefix increment operator.</dd>
 <dt>{{jsxref("Operators/Arithmetic_Operators", "--A", "#Decrement")}}</dt>
 <dd>Prefix decrement operator.</dd>
</dl>

<h3 id="Unary_operators">Unary operators</h3>

<p>A unary operation is operation with only one operand.</p>

<dl>
 <dt>{{jsxref("Operators/delete", "delete")}}</dt>
 <dd>The <code>delete</code> operator deletes a property from an object.</dd>
 <dt>{{jsxref("Operators/void", "void")}}</dt>
 <dd>The <code>void</code> operator discards an expression's return value.</dd>
 <dt>{{jsxref("Operators/typeof", "typeof")}}</dt>
 <dd>The <code>typeof</code> operator determines the type of a given object.</dd>
 <dt>{{jsxref("Operators/Arithmetic_Operators", "+", "#Unary_plus")}}</dt>
 <dd>The unary plus operator converts its operand to Number type.</dd>
 <dt>{{jsxref("Operators/Arithmetic_Operators", "-", "#Unary_negation")}}</dt>
 <dd>The unary negation operator converts its operand to Number type and then negates it.</dd>
 <dt>{{jsxref("Operators/Bitwise_Operators", "~", "#Bitwise_NOT")}}</dt>
 <dd>Bitwise NOT operator.</dd>
 <dt>{{jsxref("Operators/Logical_Operators", "!", "#Logical_NOT")}}</dt>
 <dd>Logical NOT operator.</dd>
</dl>

<h3 id="Arithmetic_operators">Arithmetic operators</h3>

<p>Arithmetic operators take numerical values (either literals or variables) as their operands and return a single numerical value.</p>

<dl>
 <dt>{{jsxref("Operators/Arithmetic_Operators", "+", "#Addition")}}</dt>
 <dd>Addition operator.</dd>
 <dt>{{jsxref("Operators/Arithmetic_Operators", "-", "#Subtraction")}}</dt>
 <dd>Subtraction operator.</dd>
 <dt>{{jsxref("Operators/Arithmetic_Operators", "/", "#Division")}}</dt>
 <dd>Division operator.</dd>
 <dt>{{jsxref("Operators/Arithmetic_Operators", "*", "#Multiplication")}}</dt>
 <dd>Multiplication operator.</dd>
 <dt>{{jsxref("Operators/Arithmetic_Operators", "%", "#Remainder")}}</dt>
 <dd>Remainder operator.</dd>
</dl>

<dl>
 <dt>{{experimental_inline}} {{jsxref("Operators/Arithmetic_Operators", "**", "#Exponentiation")}}</dt>
 <dd>Exponentiation operator.</dd>
</dl>

<h3 id="Relational_operators">Relational operators</h3>

<p>A comparison operator compares its operands and returns a <code>Boolean</code> value based on whether the comparison is true.</p>

<dl>
 <dt>{{jsxref("Operators/in", "in")}}</dt>
 <dd>The <code>in</code> operator determines whether an object has a given property.</dd>
 <dt>{{jsxref("Operators/instanceof", "instanceof")}}</dt>
 <dd>The <code>instanceof</code> operator determines whether an object is an instance of another object.</dd>
 <dt>{{jsxref("Operators/Comparison_Operators", "&lt;", "#Less_than_operator")}}</dt>
 <dd>Less than operator.</dd>
 <dt>{{jsxref("Operators/Comparison_Operators", "&gt;", "#Greater_than_operator")}}</dt>
 <dd>Greater than operator.</dd>
 <dt>{{jsxref("Operators/Comparison_Operators", "&lt;=", "#Less_than_or_equal_operator")}}</dt>
 <dd>Less than or equal operator.</dd>
 <dt>{{jsxref("Operators/Comparison_Operators", "&gt;=", "#Greater_than_or_equal_operator")}}</dt>
 <dd>Greater than or equal operator.</dd>
</dl>

<h3 id="Equality_operators">Equality operators</h3>

<p>The result of evaluating an equality operator is always of type <code>Boolean</code> based on whether the comparison is true.</p>

<dl>
 <dt>{{jsxref("Operators/Comparison_Operators", "==", "#Equality")}}</dt>
 <dd>Equality operator.</dd>
 <dt>{{jsxref("Operators/Comparison_Operators", "!=", "#Inequality")}}</dt>
 <dd>Inequality operator.</dd>
 <dt>{{jsxref("Operators/Comparison_Operators", "===", "#Identity")}}</dt>
 <dd>Identity operator.</dd>
 <dt>{{jsxref("Operators/Comparison_Operators", "!==", "#Nonidentity")}}</dt>
 <dd>Nonidentity operator.</dd>
</dl>

<h3 id="Bitwise_shift_operators">Bitwise shift operators</h3>

<p>Operations to shift all bits of the operand.</p>

<dl>
 <dt>{{jsxref("Operators/Bitwise_Operators", "&lt;&lt;", "#Left_shift")}}</dt>
 <dd>Bitwise left shift operator.</dd>
 <dt>{{jsxref("Operators/Bitwise_Operators", "&gt;&gt;", "#Right_shift")}}</dt>
 <dd>Bitwise right shift operator.</dd>
 <dt>{{jsxref("Operators/Bitwise_Operators", "&gt;&gt;&gt;", "#Unsigned_right_shift")}}</dt>
 <dd>Bitwise unsigned right shift operator.</dd>
</dl>

<h3 id="Binary_bitwise_operators">Binary bitwise operators</h3>

<p>Bitwise operators treat their operands as a set of 32 bits (zeros and ones) and return standard JavaScript numerical values.</p>

<dl>
 <dt>{{jsxref("Operators/Bitwise_Operators", "&amp;", "#Bitwise_AND")}}</dt>
 <dd>Bitwise AND.</dd>
 <dt>{{jsxref("Operators/Bitwise_Operators", "|", "#Bitwise_OR")}}</dt>
 <dd>Bitwise OR.</dd>
 <dt>{{jsxref("Operators/Bitwise_Operators", "^", "#Bitwise_XOR")}}</dt>
 <dd>Bitwise XOR.</dd>
</dl>

<h3 id="Binary_logical_operators">Binary logical operators</h3>

<p>Logical operators are typically used with boolean (logical) values, and when they are, they return a boolean value.</p>

<dl>
 <dt>{{jsxref("Operators/Logical_Operators", "&amp;&amp;", "#Logical_AND")}}</dt>
 <dd>Logical AND.</dd>
 <dt>{{jsxref("Operators/Logical_Operators", "||", "#Logical_OR")}}</dt>
 <dd>Logical OR.</dd>
</dl>

<h3 id="Conditional_(ternary)_operator">Conditional (ternary) operator</h3>

<dl>
 <dt>{{jsxref("Operators/Conditional_Operator", "(condition ? ifTrue : ifFalse)")}}</dt>
 <dd>
 <p>The conditional operator returns one of two values based on the logical value of the condition.</p>
 </dd>
</dl>

<h3 id="Assignment_operators">Assignment operators</h3>

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

<dl>
 <dt>{{jsxref("Operators/Assignment_Operators", "=", "#Assignment")}}</dt>
 <dd>Assignment operator.</dd>
 <dt>{{jsxref("Operators/Assignment_Operators", "*=", "#Multiplication_assignment")}}</dt>
 <dd>Multiplication assignment.</dd>
 <dt>{{jsxref("Operators/Assignment_Operators", "/=", "#Division_assignment")}}</dt>
 <dd>Division assignment.</dd>
 <dt>{{jsxref("Operators/Assignment_Operators", "%=", "#Remainder_assignment")}}</dt>
 <dd>Remainder assignment.</dd>
 <dt>{{jsxref("Operators/Assignment_Operators", "+=", "#Addition_assignment")}}</dt>
 <dd>Addition assignment.</dd>
 <dt>{{jsxref("Operators/Assignment_Operators", "-=", "#Subtraction_assignment")}}</dt>
 <dd>Subtraction assignment</dd>
 <dt>{{jsxref("Operators/Assignment_Operators", "&lt;&lt;=", "#Left_shift_assignment")}}</dt>
 <dd>Left shift assignment.</dd>
 <dt>{{jsxref("Operators/Assignment_Operators", "&gt;&gt;=", "#Right_shift_assignment")}}</dt>
 <dd>Right shift assignment.</dd>
 <dt>{{jsxref("Operators/Assignment_Operators", "&gt;&gt;&gt;=", "#Unsigned_right_shift_assignment")}}</dt>
 <dd>Unsigned right shift assignment.</dd>
 <dt>{{jsxref("Operators/Assignment_Operators", "&amp;=", "#Bitwise_AND_assignment")}}</dt>
 <dd>Bitwise AND assignment.</dd>
 <dt>{{jsxref("Operators/Assignment_Operators", "^=", "#Bitwise_XOR_assignment")}}</dt>
 <dd>Bitwise XOR assignment.</dd>
 <dt>{{jsxref("Operators/Assignment_Operators", "|=", "#Bitwise_OR_assignment")}}</dt>
 <dd>Bitwise OR assignment.</dd>
 <dt>{{jsxref("Operators/Destructuring_assignment", "[a, b] = [1, 2]")}}<br />
 {{jsxref("Operators/Destructuring_assignment", "{a, b} = {a:1, b:2}")}}</dt>
 <dd>
 <p>Destructuring assignment allows you to assign the properties of an array or object to variables using syntax that looks similar to array or object literals.</p>
 </dd>
</dl>

<h3 id="Comma_operator">Comma operator</h3>

<dl>
 <dt>{{jsxref("Operators/Comma_Operator", ",")}}</dt>
 <dd>The comma operator allows multiple expressions to be evaluated in a single statement and returns the result of the last expression.</dd>
</dl>

<h3 id="Non-standard_features">Non-standard features</h3>

<dl>
 <dt>{{non-standard_inline}} {{jsxref("Operators/Legacy_generator_function", "Legacy generator function", "", 1)}}</dt>
 <dd>The <code>function</code> keyword can be used to define a legacy generator function inside an expression. To make the function a legacy generator, the function body should contains at least one {{jsxref("Operators/yield", "yield")}} expression.</dd>
 <dt>{{non-standard_inline}} {{jsxref("Operators/Expression_closures", "Expression closures", "", 1)}}</dt>
 <dd>The expression closure syntax is a shorthand for writing simple function.</dd>
 <dt>{{non-standard_inline}} {{jsxref("Operators/Array_comprehensions", "[for (x of y) x]")}}</dt>
 <dd>Array comprehensions.</dd>
 <dt>{{non-standard_inline}} {{jsxref("Operators/Generator_comprehensions", "(for (x of y) y)")}}</dt>
 <dd>Generator comprehensions.</dd>
</dl>

<h2 id="Specifications">Specifications</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('ES1', '#sec-11', 'Expressions')}}</td>
   <td>{{Spec2('ES1')}}</td>
   <td>Initial definition</td>
  </tr>
  <tr>
   <td>{{SpecName('ES5.1', '#sec-11', 'Expressions')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td>&nbsp;</td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-ecmascript-language-expressions', 'ECMAScript Language: Expressions')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td>New: Spread operator, destructuring assignment, <code>super</code> keyword.</td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-ecmascript-language-expressions', 'ECMAScript Language: Expressions')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td>&nbsp;</td>
  </tr>
 </tbody>
</table>

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence">Operator precedence</a></li>
</ul>