Convert a string to number with +

Question

Here's an easy one for you true believers: You can use + to convert a string to a number,

var thing = "12"
alert(thing);
alert(typeof thing); // string
thing = +thing;
alert(typeof thing); // number
if (thing == 112) alert("!"); // number

Can someone explain:

What is the name of this process?
How does + convert a string to a number?

There you go: MDN - Arithmetic Operators - Unary Plus

Martin
– Martin

2014-04-15 11:54:44 +00:00
Commented Apr 15, 2014 at 11:54 — Martin
– Martin, Commented Apr 15, 2014 at 11:54

Gwenc37 · Accepted Answer · 2014-04-15 11:52:34Z

3

Javascript uses a dynamic type system. For me it's a 'cast' operation.

The operator + could be a String operator ('a' + 'b') or an Number operator (1+2). It could be used also between Strings and numbers (remembering that 0 + '12' = 12 and '0'+'12' = '012')

By default, i think that the JS interpreter considered +thing as 0 + things so it casts this variable to a number

answered Apr 15, 2014 at 11:52

Gwenc37

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1 Comment

Thomas Urban Over a year ago

According to developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… the target type of casting is due to the associativity of binary + being left to right ... it all starts with the type of value to the left of + requiring the other side to match type, thus requiring some type casting.

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