Operator precedence determines the way in which operators are parsed with respect to each other. Operators with higher precedence become the operands of operators with lower precedence.
Associativity
Associativity determines the way in which operators of the same precedence are parsed. 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 is 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.Examples
3 > 2 && 2 > 1
// returns true
3 > 2 > 1
// returns false because 3 > 2 is true, and true > 1 is false
// Adding parentheses makes things clear: (3 > 2) > 1Table
The following table is ordered from highest (21) to lowest (1) precedence.
| Precedence | Operator type | Associativity | Individual operators |
|---|---|---|---|
| 21 | Grouping | n/a | ( … ) |
| 20 | Member Access | left-to-right | … . … |
| Computed Member Access | left-to-right | … [ … ] | |
new (with argument list) | n/a | new … ( … ) | |
| Function Call | left-to-right | … ( … ) | |
| Optional chaining | left-to-right | ?. | |
| 19 | new (without argument list) | right-to-left | new … |
| 18 | Postfix Increment | n/a | … ++ |
| Postfix Decrement | … -- | ||
| 17 | Logical NOT | right-to-left | ! … |
| Bitwise NOT | ~ … | ||
| Unary Plus | + … | ||
| Unary Negation | - … | ||
| Prefix Increment | ++ … | ||
| Prefix Decrement | -- … | ||
typeof | typeof … | ||
void | void … | ||
delete | delete … | ||
await | await … | ||
| 16 | Exponentiation | right-to-left | … ** … |
| 15 | Multiplication | left-to-right | … * … |
| Division | … / … | ||
| Remainder | … % … | ||
| 14 | Addition | left-to-right | … + … |
| Subtraction | … - … | ||
| 13 | Bitwise Left Shift | left-to-right | … << … |
| Bitwise Right Shift | … >> … | ||
| Bitwise Unsigned Right Shift | … >>> … | ||
| 12 | Less Than | left-to-right | … < … |
| Less Than Or Equal | … <= … | ||
| Greater Than | … > … | ||
| Greater Than Or Equal | … >= … | ||
in | … in … | ||
instanceof | … instanceof … | ||
| 11 | Equality | left-to-right | … == … |
| Inequality | … != … | ||
| Strict Equality | … === … | ||
| Strict Inequality | … !== … | ||
| 10 | Bitwise AND | left-to-right | … & … |
| 9 | Bitwise XOR | left-to-right | … ^ … |
| 8 | Bitwise OR | left-to-right | … | … |
| 7 | Nullish coalescing operator | 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* | yield* … | ||
| 1 | Comma / Sequence | left-to-right | … , … |
