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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Operator: +x
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
，和
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
.
const x = 1; const y = -1; console.log(+x); // 1 console.log(+y); // -1
+true // 1
+false // 0
+null // 0
+function(val){ return val } // NaN
+1n // throws TypeError: Cannot convert BigInt value to number
| 规范 |
|---|
|
ECMAScript (ECMA-262)
The definition of 'Unary plus operator' in that specification. |
| Desktop | Mobile | Server | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Unary plus (
+
)
|
Chrome 1 | Edge 12 | Firefox 1 | IE 3 | Opera 4 | Safari 1 | WebView Android 1 | Chrome Android 18 | Firefox Android 4 | Opera Android 10.1 | Safari iOS 1 | Samsung Internet Android 1.0 | nodejs 0.1.100 |
完整支持