Unexpected result with Regular Expression in JavaScript

Question

This is my String.

 var re = "i have a string";

And this my expression

var str = re.replace(/(^[a-z])/g, function(x){return x.toUpperCase();});

I want that it will make the the first character of any word to Uppercase. But the replacement above return only the first character uppercased. But I have added /g at the last.

Where is my problem?

The `^` character means the start of the line, not the start of the word. That's the problem. — VLAZ, Jan 20 '18 at 15:45
there is an answer here : https://stackoverflow.com/questions/4878756/how-to-capitalize-first-letter-of-each-word-like-a-2-word-city — Abderrahmane TAHRI JOUTI, Jan 20 '18 at 15:47
Possible duplicate of [How to capitalize first letter of each word, like a 2-word city?](https://stackoverflow.com/questions/4878756/how-to-capitalize-first-letter-of-each-word-like-a-2-word-city) — VLAZ, Jan 20 '18 at 15:51
https://regexper.com/ paste your req exp in there and you will see why. — epascarello, Jan 20 '18 at 15:58

score 3 · Accepted Answer · edited May 04 '18 at 15:00

3

You can use the \b to mark a boundary to the expression.

const re = 'i am a string';

console.log(re.replace(/(\b[a-z])/g, (x) => x.toUpperCase()));

The metacharacter \b is an anchor like the caret and the dollar sign. It matches at a position that is called a "word boundary". This match is zero-length.

There are three different positions that qualify as word boundaries:

Before the first character in the string, if the first character is a word character.

After the last character in the string, if the last character is a word character.

Between two characters in the string, where one is a word character and the other is not a word character.

edited May 04 '18 at 15:00

AA Shakil

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answered Jan 20 '18 at 15:49

felixmosh

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Thanks Felixmosh. But could you please explain what the \b effects or it's work. – AA Shakil Jan 20 '18 at 15:52
So, do that catch expression in Every Word not line? – AA Shakil Jan 20 '18 at 16:01
Exactly, it is a "word boundary". Check out the example. – felixmosh Jan 20 '18 at 16:02

score 0 · Answer 2 · answered Jan 20 '18 at 15:48

0

Vlaz' comment looks like the right answer to me -- by putting a "^" at the beginning of your pattern, you've guaranteed that you'll only find the first character -- the others won't match the pattern despite the "/g" because they don't immediately follow the start of the line.

answered Jan 20 '18 at 15:48

Geoffrey Wiseman

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So you have a recommendation how the OP should actually solve their problem? – epascarello Jan 20 '18 at 15:59
Yeah, I should have added that -- the linked article was good, but it's better if the answer encapsulates it. Now there's already good answer, so I'll leave it. – Geoffrey Wiseman Jan 22 '18 at 15:41

Unexpected result with Regular Expression in JavaScript

2 Answers2