Unary plus (+) - JavaScript 编辑

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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Syntax

Operator: +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. 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). Using the operator on BigInt values throws a TypeError. If it cannot parse a particular value, it will evaluate to NaN.

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
+function(val){ return val } // NaN
+1n    // throws TypeError: Cannot convert BigInt value to number

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Addition operator
• Subtraction operator
• Division operator
• Multiplication operator
• Remainder operator
• Exponentiation operator
• Increment operator
• Decrement operator
• Unary negation operator