Operator precedence
Operator precedence determines the order in which operators are evaluated. Operators with higher precedence are evaluated first.
A common example:
3 + 4 * 5 // returns 23
The multiplication operator ("*
") has higher precedence than the addition operator ("+
") and thus will be evaluated first.
Associativity
Associativity determines the order in which operators of the same precedence are processed. For example, consider an expression:
a OP b OP c
Left-associativity (left-to-right) means that it is processed as (a OP b) OP c
, while right-associativity (right-to-left) means it is interpreted as a OP (b OP c)
. Assignment operators are right-associative, so you can write:
a = b = 5;
with the expected result that a
and b
get the value 5. This is because the assignment operator returns the value that it assigned. First, b
is set to 5. Then the a
is also set to 5, the return value of b = 5
, aka right operand of the assignment.
Table
The following table is ordered from highest (19) to lowest (0) precedence.
Precedence | Operator type | Associativity | Individual operators |
---|---|---|---|
19 | Grouping |
n/a | ( … ) |
18 | Member Access |
left-to-right | … . … |
Computed Member Access |
left-to-right | … [ … ] |
|
new (with argument list) |
n/a | new … ( … ) |
|
17 | Function Call | left-to-right | … ( … ) |
new (without argument list) |
right-to-left | new … |
|
16 | Postfix Increment |
n/a | … ++ |
Postfix Decrement |
n/a | … -- |
|
15 | Logical NOT | right-to-left | ! … |
Bitwise NOT | right-to-left | ~ … |
|
Unary Plus | right-to-left | + … |
|
Unary Negation | right-to-left | - … |
|
Prefix Increment | right-to-left | ++ … |
|
Prefix Decrement | right-to-left | -- … |
|
typeof | right-to-left | typeof … |
|
void | right-to-left | void … |
|
delete | right-to-left | delete … |
|
14 | Exponentiation | right-to-left | … ** … |
Multiplication | left-to-right | … * … |
|
Division | left-to-right | … / … |
|
Remainder | left-to-right | … % … |
|
13 | Addition | left-to-right | … + … |
Subtraction | left-to-right | … - … |
|
12 | Bitwise Left Shift | left-to-right | … << … |
Bitwise Right Shift | left-to-right | … >> … |
|
Bitwise Unsigned Right Shift | left-to-right | … >>> … |
|
11 | Less Than | left-to-right | … < … |
Less Than Or Equal | left-to-right | … <= … |
|
Greater Than | left-to-right | … > … |
|
Greater Than Or Equal | left-to-right | … >= … |
|
in | left-to-right | … in … |
|
instanceof | left-to-right | … instanceof … |
|
10 | Equality | left-to-right | … == … |
Inequality | left-to-right | … != … |
|
Strict Equality | left-to-right | … === … |
|
Strict Inequality | left-to-right | … !== … |
|
9 | Bitwise AND | left-to-right | … & … |
8 | Bitwise XOR | left-to-right | … ^ … |
7 | Bitwise OR | left-to-right | … | … |
6 | Logical AND | left-to-right | … && … |
5 | Logical OR | left-to-right | … || … |
4 | Conditional | right-to-left | … ? … : … |
3 | Assignment | right-to-left | … = … |
… += … |
|||
… -= … |
|||
… **= … |
|||
… *= … |
|||
… /= … |
|||
… %= … |
|||
… <<= … |
|||
… >>= … |
|||
… >>>= … |
|||
… &= … |
|||
… ^= … |
|||
… |= … |
|||
2 | yield | right-to-left | yield … |
yield* | right-to-left | yield* … |
|
1 | Spread | n/a | ... … |
0 | Comma / Sequence | left-to-right | … , … |
License
© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/javascript/reference/operators/operator_precedence