Finding location of errors in minified Javascript

Question

I am in the process of implementing a feature on a Python webserver which automatically fetches, concatenates, minifies, caches and serves Javascript files (including external ones) on first request so that users can get the benefits of minification without us having to manually run any of our Javascript through a minifier when we push changes.

However, the trouble is that our choice of minifier (slimit) introduces a syntax error somewhere in the Javascript, and (naturally) removes all newlines.

Simply knowing that there is an Unexpected token ILLEGAL somewhere in our hundreds of thousands of characters of minified Javascript is unhelpful when trying to figure out the cause of this and find a workaround.

So:

1) Is there a way, in (any) browser, that I can automatically 'prettify' Javascript when viewing it in the Developer Tools section of the browser, inserting line breaks after statements, and showing errors on the lines where they occur?

2) Alternatively, is there a clever hack I can use before returning the minified Javascript on our testing server to insert newlines at the end of statements wherever possible, in order to make it easier to find the location of the syntax error when viewing in Developer Tools?

3) Alternatively, is there some other obvious solution to my problem that I am missing?

Can you take the entire minified JS file, run it through a prettifier and then save the result for temporary testing purposes? (There are some online prettifiers like jspretty.com/...) — nnnnnn
– nnnnnn, Commented Nov 30, 2012 at 11:23
@nnnnnn Yeah, I was wondering if this would be the best solution. It'll be slightly irritating to do but should be perfectly possible. Thanks for the link to jspretty; I will try it out. — Mark Amery
– Mark Amery, Commented Nov 30, 2012 at 11:37
use 'jslint.com' before minifying, my best guess is that you forgot a ; at the end of a line. — zenpoy
– zenpoy, Commented Nov 30, 2012 at 11:41
@Mark Amery Nobody said something about re-implementing the minifier. Maybe you should check first whether it has a configuration option for such things. — feeela
– feeela, Commented Nov 30, 2012 at 12:22

Parv Sharma · Accepted Answer · 2012-11-30 11:24:35Z

3

if you are using / or can use chrome to debug then there is an option to see the minified files in pretty print
press f12 -> Sources -> Select the javascript file to debug -> select pretty print from the bottom bar.

this will set the right format will all the tabs on the minified file and probably you will be able to find the error

answered Nov 30, 2012 at 11:24

Parv Sharma

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Mark Amery Over a year ago

Sorry, should've mentioned in the question: already tried this. It does precisely nothing in my case - toggling the 'pretty print' option has no effect whatsoever on anything else. I don't know why; my best guess is that Chrome's prettify option only works on JS without syntax errors?

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