JavaScript Operators

Assignment operators were introduced in JavaScript 1.0 and Jscript 1.0.

Name	Introduced	Meaning
Assignment	JavaScript 1.0 Jscript 1.0	Sets variable v1 to the value of variable v2
Shorthand Addition or Shorthand Concatenation	JavaScript 1.0 Jscript 1.0	v1 = v1 + v2
Shorthand Subtraction	JavaScript 1.0 Jscript 1.0	v1 = v1 - v2
Shorthand Multiplication	JavaScript 1.0 Jscript 1.0	v1 = v1 * v2
Shorthand Division	JavaScript 1.0 Jscript 1.0	v1 = v1 / v2
Shorthand Modulus	JavaScript 1.0 Jscript 1.0	v1 = v1 % v2
Shorthand left shift	JavaScript 1.0 Jscript 1.0	v1 = v1 << v2
Shorthand right shift	JavaScript 1.0 Jscript 1.0	v1 = v1 >> v2
Shorthand zero fill right shift	JavaScript 1.0 Jscript 1.0	v1 = v1 >>> v2
Shorthand AND	JavaScript 1.0 Jscript 1.0	v1 = v1 & v2
Shorthand XOR	JavaScript 1.0 Jscript 1.0	v1 = v1 ^ v2
Shorthand OR	JavaScript 1.0 Jscript 1.0	v1 = v1 \| v2

Comparison operators were first introduced in JavaScript 1.0, though a few changes have been made as noted. If v1=1 and v2=2, the following example statements are all true. Boolean literal values true and false are returned by the comparisons.

In JavaScript 1.4, == has been deprecated with respect to objects in favor of JSObject.equals. In JavaScript 1.2 only, neither == nor !== attempted type conversion before returning a value.

Name	Introduced	Meaning
Equal	JavaScript 1.0 Jscript 1.0	True if two operands are strictly equal or equal once cast to the same type.
Not Equal	JavaScript 1.0 Jscript 1.0	True if two operands are not strictly equal or not equal once cast to the same type.
Greater Than	JavaScript 1.0 Jscript 1.0	True if LHS operand is greater than RHS operand.
Greater Than Or Equal	JavaScript 1.0 Jscript 1.0	True if LHS operand is greater than or equal to RHS operand.
Less Than	JavaScript 1.0 Jscript 1.0	True if LHS operand is less than RHS operand.
Less Than Or Equal	JavaScript 1.0 Jscript 1.0	True if LHS operand is less than or equal to RHS operand.
Strictly Equal	JavaScript 1.3 Jscript 1.0	Not in ECMA-262. True if operands are equal and of same type.
Not Strictly Equal	JavaScript 1.3 Jscript 1.0	Not in ECMA-262. True if operands are not strictly equal.

Arithmetic operators were first introduced in JavaScript 1.0 and Jscript 1.0.

Name	Introduced	Result
Addition	JavaScript 1.0 Jscript 1.0	Sum of v1 and v2 concatenation of v1 and v2, if they are strings.
Subtraction	JavaScript 1.0 Jscript 1.0	Difference of v1 and v2.
Multiplication	JavaScript 1.0 Jscript 1.0	Product of v1 and v2.
Division	JavaScript 1.0 Jscript 1.0	Quotient of v2 into v1.
Modulus	JavaScript 1.0 Jscript 1.0	Integer remainder of
Prefix Increment	JavaScript 1.0 Jscript 1.0	(v1 + 1) * v2. Note: v1 will be left as v1 + 1.
Postfix Increment	JavaScript 1.0 Jscript 1.0	(v1 * v2); v1 is then incremented by 1.
Prefix Decrement	JavaScript 1.0 Jscript 1.0	(v1 – 1) * v2. Note: v1 is left as v1 - 1.
Postfix Decrement	JavaScript 1.0 Jscript 1.0	(v1 * v2). v1 is then decremented by 1.

Bitwise logical operators were first introduced in JavaScript 1.0 and Jscript 1.0. They work by converting values in v1 and v2 to 32-bit binary numbers and then comparing the individual bits of these two binary numbers. The result is returned as a normal decimal number.

Name	Introduced	Result
Bitwise AND	JavaScript 1.0 Jscript 1.0	The bitwise AND is true only when both bits are set.
Bitwise OR	JavaScript 1.0 Jscript 1.0	The bitwise OR is true if either bits are set.
Bitwise XOR	JavaScript 1.0 Jscript 1.0	The Bitwise XOR returns a one in each bit position for which the corresponding bits of either but not both operands are ones.
Bitwise NOT	JavaScript 1.0 Jscript 1.0	Inverts all the bits in the number.

Bitwise shift operators were first introduced in JavaScript 1.0 and Jscript 1.0. They work by converting values in v1 to 32-bit binary numbers and then moving the bits in the number to the left or the right by the specified number of places.

Name	Introduced	Result
Left Shift	JavaScript 1.0 Jscript 1.0	Shifts v1 to the left by v2 places, filling the new gaps in with zeros.
Right Shift	JavaScript 1.0 Jscript 1.0	Shifts v1 to the right by v2 places, ignoring the bits shifted off the number.
Sign Propagating Right Shift	JavaScript 1.4 Jscript 1.0	Shifts v1 to the right by v2 places, ignoring the bits shifted off the number.
Zero-fill Right Shift	JavaScript 1.0 Jscript 1.0	Shifts v1 to the right by v2 places, ignoring the bits shifted off the number and adding v2 zeros to the left of the number.

Logical operators were first introduced in JavaScript 1.0 and Jscript 1.0. They should return one of the Boolean literals, true or false. However, this may not happen if either v1 or v2 is neither a Boolean value nor a value that easily converts to a Boolean value, such as 0, 1, null, the empty string, or undefined.

Name	Introduced	Result
Logical AND	JavaScript 1.0 Jscript 1.0	Returns true if both v1 and v2 are true, false otherwise. Will not evaluate v2 if v1 is false.
Logical OR	JavaScript 1.0 Jscript 1.0	Returns false if both v1 and v2 are false, true otherwise. Will not evaluate v2 if v1 is true.
Logical NOT	JavaScript 1.0 Jscript 1.0	Returns false if v1 is true, true otherwise.

Several operators have been introduced to JavaScript to deal with objects.

Name	Introduced	Description
delete	JavaScript 1.2 Jscript 3.0	Deletes an object, one of its properties or the element of an array at the specified index.
in	JavaScript 1.4	Not in ECMA-262. Returns true if someObject has the named property. Not supported by Internet Explorer.
instanceof	JavaScript 1.4 Jscript 5.0	Not in ECMA-262. Returns true if someObject is of type objectType.
new	JavaScript 1.0 Jscript 1.0	Creates a new instance of an object with type objectType. The parameterList obeys a constructor function specified elsewhere.
this	JavaScript 1.0 Jscript 1.0	Refers to the current object.

JavaScript has several other miscellaneous operators.

Name	Introduced	Description
Conditional Operator	JavaScript 1.0 Jscript 1.0	If evalquery is true, the operator returns v1, else it returns v2.
Comma Operator	JavaScript 1.0 Jscript 1.0	Evaluates both eval1 and eval2 while treating the two as one expression.
typeof	JavaScript 1.1 Jscript 1.0	Returns a string holding the type of v1, which is not evaluated.
void	JavaScript 1.1 Jscript 2.0	Evaluates eval1 but does not return a value.

Operator Precedence

Does 1 + 2 * 3 = 1 + (2 * 3) = 7 or does it equal (1 + 2) * 3 = 9?

The ECMAScript standard doesn't yet clearly document operator precedence. However, JavaScript closely follows Java, and Java closely follows C. The following table shows precedence with the highest at the top, and like operators grouped together. The third column explains whether to read 1+2+3+4 as ((1+2)+3)+4 or 1+(2+(3+(4))).

Operator Type	Operators	Evaluation Order for Like Elements
comma	,	left to right
Conditional	? :	left to right
postfix operators	[] () . expr++ expr—	left to right
unary operators	++expr —expr +expr -expr ~ !	right to left
object management or cast	delete new typeof void	right to left
multiplicative	* / %	left to right
additive/subtractive	+ -	left to right
negation/increment	! ~ - + ++ — typeof void delete	left to right
Call	()	left to right
shift	<< >> >>>	left to right
relational	< > <= >= in instanceof	left to right
equality	== != === !==	left to right
bitwise AND	&	left to right
bitwise exclusive OR	^	left to right
Bitwise shift	<< >> >>>	left to right
bitwise OR	\|	left to right
logical AND	&&	left to right
logical OR	\|\|	left to right
conditional	? :	right to left
assignment	= += -= &= <<= >>== &= ^= \|=	right to left
multiple evaluation	,	left to right
create instance	new