do I need eval?

Question

I've searched the web for what eval does and here is what I have found:

The eval() method evaluates JavaScript code represented as a string.

And I've read this question, which says that it is evil.
But I really don't understand what does it do, i.e I don't see when to use eval.
I mean:

var x= 3;
var y =5;
var z = eval("x+y");
// is the same as:
var z = x+y;

so as I see it's just adding characters to my code. Can somebody give me an example of why eval was created in the first place?

@user689: Check out this question: http://stackoverflow.com/questions/9089532/why-does-eval-exist :-D — gen_Eric, Jan 03 '14 at 19:28

score 3 · Accepted Answer · answered Jan 03 '14 at 19:24

3

It allows execute dynamicly generated code, not just "x+y".

answered Jan 03 '14 at 19:24

Daniil Grankin

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can you give an example? – Jan 03 '14 at 19:25
1

I think it is not bad example for using it http://jsfiddle.net/ondras/hYfN3/ – Daniil Grankin Jan 03 '14 at 19:31
It possible to avoid use it but sometimes using it is the easiest solution. – Daniil Grankin Jan 03 '14 at 19:33

score 1 · Answer 2 · answered Jan 03 '14 at 19:39

Eval allows you to evaluate a string as javascript code. This means you can do things like evaluate a string to call a function:

function add(x,y){
     return (x+y);
}

stringToEval = 'add(5,6)';

eval(stringToEval);

This code would run the function by evaluating the string as a function call. So I would say you do not need to use eval here. Just add the two variables.

do I need eval?

2 Answers2