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I have both es5-shim.js and underscore.js in my JavaScript project.

es5-shim.js just add some javascript native functions like reduce and some on arrays for Internet Explorer and some old browsers. underscore.js add the same thing (but with a different syntax) and many more thing (utility functions on objects and arrays).

But, if the functions added by es5-shim exists, underscore.js use them.

So, on a "recent" browser like Firefox or Chrome, underscore.js use the native functions of the browser. I think it's better than a pure javascript function. But on Internet Explorer, underscore.js use the es5-shim functions. If I remove es5-shim.js, underscore.js use its own functions.

Any advice on that ? Should i remove es5-shim from my project and only use underscore.js ? Or should i let underscore.js use es5-shim's functions ?

mikemaccana
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Magus
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  • Are those function implementations actually functionally different? Does es5-shim add something underscore does not? – DCoder Nov 24 '12 at 11:54
  • @DCoder The behavior is exactly the same. And if i only use underscore.js functions, the syntax is exactly the same (for example : _.each(myArray, function() { //Do some stuff }); ). So the only problem could be some performance problems or maybe some bugs in es5-shim i don't know. – Magus Nov 24 '12 at 11:56
  • If es5-shim adds something underscore does not, you should keep it. Otherwise, my first thought would be to get rid of it, but you might want to see if both approaches score the same on the es5 test suite (you might need to fiddle around with that to include the shim/underscore in the testing). – DCoder Nov 24 '12 at 12:03
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    @DCoder It's pretty hard to run es5 test suite on underscore.js alone. Because underscore.js does not create function in the "native style". So on Internet explorer with only underscore.js, Array.some does not exists, but _.some(myArray, ...) exists. – Magus Nov 24 '12 at 12:42

2 Answers2

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I disagree with @ganeshi's answer.

If your primary use of Underscore is things that already come with ES5 like reduce() and some() then I suggest you remove underscore.js.

If you code to ES5 methods now, you can simply remove ES5-shim when you no longer support IE8 or Firefox 3.

If you use underscore now, then when you no longer support IE8 or Firefox 3 you still will carry an extra copy of a large amount of things most browsers already provide.

Community
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mikemaccana
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es5-shim, as you rightly mentioned, adds some JavaScript functions like map, reduce, some and forEach on Array if the browser's JavaScript engine is not ES5 compatible. Underscore.js adds utility methods similar to the above (and more) within the "_" namespace. So, in this case, using both in the same application is redundant.

That said, es5-shim, adds a few more functions like Date.now, Date.toJSON, Function.bind, String.trim (and more) some which don't have direct equivalents in Underscore.js. For example Underscore does provide _.bind and _.bindAll that is equivalent to Function.bind, but Underscore.js does not provide Date.now and Date.toJSON.

So, if you use these additional methods provided by es5-shim you can stay with both es5-shim and Underscore.js in your application. But, if you are not using these additional methods, then using es5-shim would just be an unnecessary increase in application size and waste of bandwidth.

Ganeshji Marwaha
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