Built-in operators

Javascript offers built-in operators in the following categories:

Assignment operators
Arithmetic operators
String operators
Logical operators
Comparison operators
Bit-wise operators
Special operators

Assignment operators

These operators are used to assign the value of expressions to variables.

= operator

var variable = expression;

The assignment operator is used to assign the value of an expression to the variable.

It is an error to attempt to assign to a constant.

+= operator

variable += expression;

This operator adds the value of the expression to the variable. It is the same as:

 variable = variable + expression;

but is shorter to write and less error-prone.

Arithmetic operators

These operators are used to perform arithmetic computations on their operands.

+ operator

operand1 + operand2

This operator returns the result of adding the two operands (operand1 and operand2).

String operators

These operators provide string functions using operators. Many other string functions are available, see String.

+ string operator

str1 + str2

This operator returns a string that is the concatenation of its operands, (str1 and str2).

Logical operators

These operators are used to evaluate whether their operands are true or false. The binary operators use short-circuit logic, that is, they do not evaluate their second operand if the logical value of the expression can be determined by evaluating the first operand alone.

&& operator

operand1 && operand2

This operator returns an object whose value is true if both its operands are true; otherwise it returns an object whose value is false.

Specifically, if the value of operand1 is false, the operator returns operand1 as its result. If operand1 is true, the operator returns operand2.

|| operator

operand1 || operand2

This operator returns an object whose value is true if either of its operands are true; otherwise it returns an object whose value is false.

Specifically, if the value of operand1 is true, the operator returns operand1 as its result. If operand1 is false, the operator returns operand2.

! operator

! operand

If the operand's value is true, this operator returns false; otherwise it returns true.

Comparison operators

These operators are used to compare objects and their values.

== operator

operand1 == operand2

Returns true if the operands are equal; otherwise returns false.

!= operator

	operand1 != operand2

Returns true if the operands are not equal; otherwise returns false.

=== operator

operand1 === operand2

Returns true if the operands are equal and of the same type; otherwise returns false.

!== operator

operand1 !== operand2

Returns true if the operands are not equal or if the operands are of different types;otherwise returns false.

> operator

operand1 > operand2

Returns true if operand1 is greater than operand2; otherwise returns false.

>= operator

operand1 >= operand2

Returns true if operand1 is greater than or equal to operand2; otherwise returns false.

< operator

operand1 < operand2

Returns true if operand1 is less than operand2; otherwise returns false.

<= operator

operand1 <= operand2

Returns true if operand1 is less than or equal to operand2; otherwise returns false.

Bit-wise operators

& operator

operand1 & operand2

Returns the result of a bit-wise AND on the operands (operand1 and operand2).

^ operator

operand1 ^ operand2

Returns the result of a bit-wise XOR on the operands (operand1 and operand2).

| operator

operand1 | operand2

Returns the result of a bit-wise OR on the operands (operand1 and operand2).

~ operator

~ operand

Returns the bit-wise NOT of the operand.

<< operator

operand1 << operand2

Returns the result of a bit-wise left shift of operand1 by the number of bits specified by operand2. Zeros are shifted in from the right.

>> operator

operand1 >> operand2

Returns the result of a bit-wise (sign propagating) right shift of operand1 by the number of bits specified by operand2.

>>> operator

operand1 >>> operand2

Returns the result of a bit-wise (zero filling) right shift of operand1 by the number of bits specified by operand2. Zeros are shifted in from the left.

Special operators

?: operator

expression ? resultIfTrue : resultIfFalse

This operator evaluates its first operand, the expression. If the expression is true, the value of the second operand (resultIfTrue) is returned; otherwise the value of the third operand (resultIfFalse) is returned.

, operator

expression1, expression2

This operator evaluates its first and second operand (expression1 and expression2) and returns the value of the second operand (expression2).

The comma operator can be subtle and is best reserved only for use in argument lists.

function operator

var variable = function( optArguments ) { Statements }

This operator is used to create anonymous functions. Once assigned, the variable is used like any other function name, example variable (1, 2, 3). Specify the argument names (in optArguments) if named arguments are required. If no optArguments are specified, arguments may still be passed and will be available using the arguments list.

The JavaScript function operator supports closures, for example:

    function make_counter( initialValue ) 
    { 
        var current = initialValue; 
        return function( increment ) { current += increment; return current; } 
    } 
    // ... 
    var counterA = make_counter( 3 );  // Start at 3. 
    var counterB = make_counter( 12 ); // Start at 12. 
    var x1 = counterA( 2 );  // Adds 2, so x1 == 5 
    var x2 = counterB( 2 );  // Adds 2, so x2 == 14 
    var x3 = counterA( 7 );  // Adds 7, so x3 == 12 
    var x4 = counterB( 30 ); // Adds 30, so x4 ==44

Note that for each call to make_counter(), the anonymous function that is returned has its own copy of current (initialized to the initialValue), which is incremented independently of any other anonymous function's current. It is this capturing of context that makes the function that is returned a closure.

See also function declaration and Function type.

in operator

property in Object

Returns true if the given Object has the given property; otherwise returns false.

instanceof operator

object instanceof type

Returns true if the given object is an instance of the given type, (or of one of its base classes); otherwise returns false.

new operator

var instance = new Type( optArguments );

This function calls the constructor for the given Type, passing it the optional arguments (optArguments) if any and returns an instance of the given Type. The Type may be one of the built-in types, one of the library types, or a user-defined type.

Example:

    var circle = new Circle( x, y ); 
    var file = new File();

this operator

this.property

The "this" operator may only be used within a function that is defined within a class, that is a member function. Within the scope of the function this is a reference to the particular instance (object) of the class's type.

Example:

    class MinMax { 
        var _min; 
        var _max; 
        function MinMax( min, max ) { this._min = min; this._max = max; } 
        function max() { return this._max; } 
        function min() { return this._min; } 
        function setMax( value ) { this._max = value; } 
        function setMin( value ) { this._min = value; } 
    }

typeof operator

typeof item

This operator returns a type of the object as a string.

Example:

    var f = new Function("arguments[0]*2"); // "object" 
    var str = "text"; // "string" 
    var pi = Math.PI; // "number"

Functions and built-in objects have a "typeof" of "function".