Question

I have encountered something weird (probably not, it’s more likely that I don’t really get it) in JavaScript and I’d be curious to find out why things behave like they do.

When I do:

var index = '1';
index++;
alert(index);
index = index + 1;
alert(index);
index = true ? index + 1 : 0;
alert(index);

as in http://jsfiddle.net/5mdmJ/ the alerts will go “2”, “3”, “4”

When I reverse the order and do this (http://jsfiddle.net/5mdmJ/1/):

var index = '1';
index = true ? index + 1 : 0;
alert(index);
index = index + 1;
alert(index);
index++;
alert(index);

I’ll have “11”, “111” and “112”.

I do know that this is something with index being a string, but I don’t really get why it’s int-typed all the way through in example 1 and string-typed in exampled two.
I know this is probably going to be really simple but I could not find anything by now that really clarifies to me the logic behind what’s going on. Does the type change? Why and when does this happen?

Thanks for any hint or article or whatever!

Answer 1

The answer is that since js is loosely typed it starts with the first operation that youre performing.

In your example 1 the first operation is an exclusive arithmetic operation and js correctly interprets it and considers it INT all the way

In your example 2 the first operation is an comparsion operation and js interprets it as boolean and then its immediately close property string.

Thats why you get different behaviours.