Unary plus (+)

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.

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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.


Usage with numbers

const x = 1;
const y = -1;

// 1
// -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


ECMAScript Language Specification
# sec-unary-plus-operator

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See also