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:

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

Answer 1

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