JavaScript Regex: Number of trailing newlines in a string

Question

I'm trying to find the number of trailing newlines in a string. Consider the following example:

var foo = 'bar \n fooo \n   \n   \n';

For foo i should get back 3, meaning it won't count the newline between bar and fooo.

The way that I'm doing it right now is matching all trailing whitespaces /\s*$. and then matching /\n/g against the result to get the exact number. While this works, I was wondering if there is a way to do it with only one regular expression. Thanks for you help!

P.S.

Assume that all newlines are normalized to \n.

p.s.w.g · Accepted Answer · 2013-11-18 23:41:03Z

1

You could use /\s+$/ to find all trailing whitespace, then count the number of \n found in that string.

For example:

var foo = 'bar \n fooo \n   \n   \n';
var trailingLines = foo .match(/\s+$/)[0].split('\n').length - 1;

Alternatively, you could use a lookahead in a pattern like this:

/\n(?=\s*$)/g

This will match any \n which is followed by zero or more whitespace characters and the end of the string.

For example:

var foo = 'bar \n fooo \n   \n   \n';
var trailingLines = foo.match(/\n(?=\s*$)/g).length;

answered Nov 18, 2013 at 23:41

p.s.w.g

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lordkain · Accepted Answer · 2013-11-18 23:51:06Z

1

(\s*\n\s*)+$

\s* matches zero or more whitespaces

'your string here'.match(/(\s*\n\s*)+$/g).length;

edited Nov 18, 2013 at 23:51

answered Nov 18, 2013 at 23:38

lordkain

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1 Comment

p.s.w.g Over a year ago

This code doesn't work. 'bar \n fooo \n \n \n'.match(/(\s*\n\s*)+$/g).length returns 1, but OP expects 3.

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