Operator Precedence in Javascript

Operator precedence includes unary, increment, basic arithmetic, logical and assignment operators - roughly in that order.

The precedence can be remembered by BEUDMASLAS.

brackets
exponent
unary & prefixed increment / decrement
division
multiplication
addition
subtraction
logical
assignment
suffixed increment / decrement

Not quite exciting as BODMAS or PEDMAS (math, anyone?) and as it turns out - you would not even have to remember it :).

An outline with examples is below.

Type	Operator	Description	Example
Brackets	`(` `)`	Two brackets to rule them all	`10 / (2+3)`
Exponential	`**`		`2 ** 2`
Unary & friends	`+` `-` `++` `--`	Unary operators, pre increment/decrement	`++i`, `-j`
Arithmetic	`%` `*`	Binary arithmetic operations	`i / j`
Arithmetic	`+` `-`	Needs no explanation	`i + j`
Logical	`!` `&&` \|\|	Logical operators in order of precedence	`i && !j`
Assignment	`+=` `-=` `*=` `/=`		`i += 1`
Assignment	`=`	Let there be assignment (at the end)
Post incr./decr.	`++` `--`	Changed value available to next operation	`i++`

Golden rule: put brackets whenever in doubt.

Priceless rule: Use prettier (and you should). It will automatically put brackets to clarify precedence and make the expression readable.

Let us look at some examples -

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28


let [x, y, z] = [1, 3, 5];

console.log(x / y + z); // 5.33

console.log(x + (x * y) / z ** 2); // 1.12

console.log(x + y * ++z); // 19
z--; //reset z to 5

console.log(x + y * z++); // 16. z is incremented after the entire operation
console.log(z); // 16

z = 5; //reset z to 5

console.log((z = x + y * z++)); // 16. z is incremented after the entire operation
console.log("reassigned:", z); // reassigned: 16

z = 5; //reset z to 5

console.log(i || (j && !k)); // true

console.log(1 + 5 / 2 && true); // true, since 3 = true

x = y += 1;
console.log(x, y); // 4 4

x = z *= 1 + 1;
console.log(x, z); // 10 10

Operator Precedence in Javascript

See Also