return "1"; // returns string
return +"1"; // returns int
I'd like to know what this method is called when using +"n" to convert from string to int.
4 Answers
It's just the intrinsic type coercion that the unary + operator performs according to the language spec.
- Let expr be the result of evaluating UnaryExpression.
- Return ToNumber(GetValue(expr)).
So although conceptually it's just the opposite of unary -, since a + operation just means "multiply by positive 1" the only real work that's done is to coerce the value to a number.
Comments
From MDN:
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. 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.
Examples:
+3 // 3 +"3" // 3 +true // 1 +false // 0 +null // 0
4 Comments
BoltClock
This is lifted from developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…, but with the sentences separated into paragraphs... for some reason.
Josh Crozier
Plagiarized from developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… .. copied text should be placed within blockquotes, and you should link to the source
BoltClock
Don't try to sidestep the issue. You need to cite your sources. That is a rule. See meta.stackexchange.com/questions/160077/…
a-d
@CatalinMunteanu no that's not the problem I think, juste cite the sources, it gives the impression you try to somehow hide this information, even though it is probably not the case
You are using the unary operator + which tries to cast anything to its right to a Number (as a float).
Note that it may return NaN if it can't be cast to a Number.
Similarly you can use parseFloat, which may return NaN as well
parseFloat(anyValue, 10);
Comments
You're applying the unary operator +.
It's not defined for string, so JS has to convert the string to a number first.
Of course, be careful not to accidentally turn it into a binary operator. It's not something you want to use in real code, because it's kind of fragile :)
+is being interpreted as "make this value positive"-type operation. a "negative string" doesn't exist, so the string-1 gets coerced to an int. it'd be no different if you hadreturn -"1", except you'd get a negative back instead