Unary plus (+)
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
The unary plus (+) operator precedes its operand and evaluates to its
operand but attempts to convert it into a number, if it isn't already.
Try it
const x = 1;
const y = -1;
console.log(+x);
// Expected output: 1
console.log(+y);
// Expected output: -1
console.log(+"");
// Expected output: 0
console.log(+true);
// Expected output: 1
console.log(+false);
// Expected output: 0
console.log(+"hello");
// Expected output: NaN
Syntax
+x
Description
Although unary negation (-) also can convert non-numbers, unary plus is the fastest and preferred way of converting something into a number, because it does not perform any other operations on the number.
Unary plus does the exact same steps as normal number coercion used by most built-in methods expecting numbers. It can convert string representations of integers and floats, as well as the non-string values true, false, and null. Integers in both decimal and hexadecimal (0x-prefixed) formats are supported. Negative numbers are supported (though not for hex). If it cannot parse a particular value, it will evaluate to NaN. Unlike other arithmetic operators, which work with both numbers and BigInts, using the + operator on BigInt values throws a TypeError.
Examples
Usage with numbers
const x = 1;
const y = -1;
console.log(+x);
// 1
console.log(+y);
// -1
Usage with non-numbers
+true // 1
+false // 0
+null // 0
+[] // 0
+function (val) { return val; } // NaN
+1n // throws TypeError: Cannot convert BigInt value to number
Specifications
| Specification |
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| ECMAScript® 2027 Language Specification # sec-unary-plus-operator |
Browser compatibility
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Unary plus (
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Legend
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- Full support
- Full support