What's the main benefit of using eval() in JavaScript?

javascript eval
Caffeinated picture Caffeinated · May 6, 2012 · Viewed 41.6k times · Source

I know this may be a newbie question, but I'm curious as to the main benefit of eval() - where would it be used best? I appreciate any info.

Answer

Guffa picture Guffa · May 6, 2012

The eval function is best used: Never.

It's purpose is to evaluate a string as a Javascript expression. Example:

eval('x = 42');

It has been used a lot before, because a lot of people didn't know how to write the proper code for what they wanted to do. For example when using a dynamic name for a field:

eval('document.frm.'+frmName).value = text;

The proper way to do that would be:

document.frm[frmName].value = text;

As the eval method executes the string as code, every time that it is used is a potential opening for someone to inject harmful code in the page. See cross-site scripting.

There are a few legitimate uses for the eval function. It's however not likely that you will ever be in a situation where you actually will need it.

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