Mozilla Developer NetworkSummary
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 set to the value of b.
Table
The following table is ordered from highest (1) to lowest (18) precedence.
| Precedence | Operator type | Associativity | Individual operators |
|---|---|---|---|
| 1 | member | left-to-right | . |
| [] | |||
| new | right-to-left | new | |
| 2 | FIXME: function call | left-to-right | () |
| 3 | increment | n/a | ++ |
| decrement | n/a | -- | |
| 4 | logical-not | right-to-left | ! |
| bitwise not | right-to-left | ~ | |
| unary + | right-to-left | + | |
| unary negation | right-to-left | - | |
| typeof | right-to-left | typeof | |
| void | right-to-left | void | |
| delete | right-to-left | delete | |
| 5 | multiplication | left-to-right | * |
| division | left-to-right | / | |
| modulus | left-to-right | % | |
| 6 | addition | left-to-right | + |
| subtraction | left-to-right | - | |
| 7 | bitwise shift | left-to-right | << |
| >> | |||
| >>> | |||
| 8 | relational | left-to-right | < |
| <= | |||
| > | |||
| >= | |||
| in | left-to-right | in | |
| instanceof | left-to-right | instanceof | |
| 9 | equality | left-to-right | == |
| != | |||
| === | |||
| !== | |||
| 10 | bitwise-and | left-to-right | & |
| 11 | bitwise-xor | left-to-right | ^ |
| 12 | bitwise-or | left-to-right | | |
| 13 | logical-and | left-to-right | && |
| 14 | logical-or | left-to-right | || |
| 15 | conditional | right-to-left | ?: |
| 16 | yield | right-to-left | yield |
| 17 | assignment | right-to-left | = |
| += | |||
| -= | |||
| *= | |||
| /= | |||
| %= | |||
| <<= | |||
| >>= | |||
| >>>= | |||
| &= | |||
| ^= | |||
| |= | |||
| 18 | comma | left-to-right | , |