Javascript eval() not working with passed string

Question

My code snippet:

function receive(mag)
{
    var text = eval(mag);
    alert(text);
}

receive('["magnolia,", ["Magnolia (Flower)"], [], [], [], [], [], [[3, 19019, "INV_MAG_39 ", 5]]]');

When I pass the string in the example (shown above), the eval(mag) doesn't work. But if I do it directly like this:

function receive(mag)
{
    var text = eval('["magnolia,", ["Magnolia (Flower)"], [], [], [], [], [], [[3, 19019, "INV_MAG_39 ", 5]]]');
    alert(text);
}

It does work. Does anyone have an idea whats wrong / how can I get it working with passed variable?

What does "won't work" mean? What actually happens with the first version? (Do you get any errors in the console?) — nnnnnn
– nnnnnn, Commented Sep 11, 2012 at 22:43
Because eval will execute anything inside the string, and since it only makes sense to eval external data, it is potentially very dangerous. — Aesthete
– Aesthete, Commented Sep 11, 2012 at 22:49

frenchie · Accepted Answer · 2012-09-11 22:47:47Z

4

I think you're missing the parenthesis:

eval('(' + mag + ')')

But why not use JSON.parse??

var text = JSON.parse(mag);

edited Sep 11, 2012 at 22:47

answered Sep 11, 2012 at 22:45

frenchie

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8 Comments

nnnnnn Over a year ago

Why do the parentheses matter when including the string directly works without them? (And even the "broken" code works fine for me here: jsfiddle.net/HvrzK - tested with Chrome.)

xtra Over a year ago

Well, i've only included like-code because the original is too long to post. But you get my point; what it does in real code is get string with ajax and pass it to a function.

frenchie Over a year ago

@nnnnnn: yes, you're right arrays too. Anyway, the correct syntax is eval('(' + mag + ')')

frenchie Over a year ago

What's not working? What error are you getting? The syntax is correct so if you're not getting the result you want, the problem is elsewhere.

Jay Over a year ago

@xtra: Check the web browser's console log. It'll give you the exact cause of error on the exact string passed to the receive function. The string from your example does work, so it's likely that the error occured on a different string.

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