Why is this defensive semicolon used?

Question

In the lodash library line, why is there a defensive semicolon on the first line?

;(function(window) {
    ...
}(this));

I recently read in Definitive JavaScript about defensive semicolons being used to protect against users who don't use semicolons properly, but as there is no preceding code, I don't see the point. Is this in case the library is concatenated on to the end of another library?

A simple YES is the answer to your question (at the end). :-) — Mario, Jul 09 '13 at 14:08
possible duplicate of [What does the leading semicolon in JavaScript libraries do?](http://stackoverflow.com/questions/1873983/what-does-the-leading-semicolon-in-javascript-libraries-do) — freejosh, Jul 09 '13 at 14:09

karthikr · Answer 1 · 2013-07-09T14:10:04.583

6

In case you use a javascript compressor/minifier, and the previous plugin does not have a ; at the end, you might run into troubles. So, as a precaution, ; is added.

Also, It safely allows you to append several javascript files, to serve it in a single HTTP request.

edited Jul 09 '13 at 14:10

answered Jul 09 '13 at 14:04

karthikr

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score 0 · Answer 2 · edited May 23 '17 at 12:17

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That semicolon is also used to ensure that it is not interpreted as a continuation of the previous statement:

var x = 0 // Semicolon omitted here
;[x,x+1,x+2].forEach(console.log) // Defensive ; keeps this statement separate

More detail: https://stackoverflow.com/a/20854706/1048668

edited May 23 '17 at 12:17

Community

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answered Sep 24 '14 at 04:20

voltrevo

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Why is this defensive semicolon used?

2 Answers2