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What does the JavaScript [+num] syntax do?

Tags:

javascript

I have come across a refernce to a JavaScript syntax that I don't understand and cannot find any references to online.

[+num]

What does this syntax do and when is it used?

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John Haager Avatar asked Oct 20 '25 15:10

John Haager


1 Answers

It forces a conversion to a number.

  +'0'; // 0
  +[]; // 0
  +true; // 1
  +false; // 0
  +"I'm Not A Number"; // NaN

From Operators: https://developer.mozilla.org/en/JavaScript/Reference/Operators/Arithmetic_Operators#.2b_(Unary_Plus)

+ (Unary Plus)

The unary plus operator precedes its operand and evaluates to its operand but attempts to converts it into a number, if it isn't already. For example, y = +x takes the value of x and assigns that to y; that is, if x were 3, y would get the value 3 and x would retain the value 3; but if x were the string "3", y would also get the value 3. 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). If it cannot parse a particular value, it will evaluate to NaN.

like image 168
Joe Avatar answered Oct 22 '25 04:10

Joe



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