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One of our legacy JavaScript code contains this line of code:

code.match(/if\\s*\\(/g).length

What does this /if\\s*\\(/g regex mean?

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    this will show you an error. Commented Feb 16, 2015 at 6:03

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It means match "if" followed by whitespace "zero or more" times and an open parentheses. Except it should error because of the double escapes, the regular expression would be:

code.match(/if\s*\(/g).length

A regular expression literal does not use double escapes, they're used in RegExp Objects.

var re = new RegExp('if\\s*\\(', 'g') code.match(re).length;

In other words:

Regular expression visualization

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2 Comments

It all makes sense now. Not sure why it has double escapes. Thank you.
Double escapes can be valid. It just changes the meaning to: i followed by f followed by \ followed by zero or more s then \(
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The match() method searches a string for a match against a regular expression, and returns the matches, as an Array object.

Search a string for "ain":

 var str = "The rain in SPAIN stays mainly in the plain"; var res = str.match(/ain/g);

The result of res will be an array with the values:

 ain,ain,ain

See more: http://www.w3schools.com/jsref/jsref_match.asp

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