CODEWITHSUNDEEP
javascriptregex
user9258655
user9258655

Reputation:

Same results with \b meta character with it vs without it

I'm learning regular expressions in JavaScript and the problem I am facing is i'm trying to understand why the \b meta character is so special to use? I see no difference by not using it vs using it so what is the difference between using it and not using it? This is what I mean.

WITH \b

<!DOCTYPE html>
<html>
<body>

<p>Click the button to do a global search for "W3" at the beginning or end of a word in a string.</p>

<button onclick="myFunction()">Try it</button>

<p id="demo"></p>

<script>
function myFunction() {
    var str = "Visit W3Schools"; 
    var patt1 = /\bW3/g;
    var result = str.match(patt1);
    document.getElementById("demo").innerHTML = result;
}
</script>

</body>
</html>

WITH OUT \b

<!DOCTYPE html>
<html>
<body>

<p>Click the button to do a global search for "W3" at the beginning or end of a word in a string.</p>

<button onclick="myFunction()">Try it</button>

<p id="demo"></p>

<script>
function myFunction() {
    var str = "Visit W3Schools"; 
    var patt1 = /W3/g;
    var result = str.match(patt1);
    document.getElementById("demo").innerHTML = result;
}
</script>

</body>
</html>

I already know what it means by definition by reading it but i'm simply just questioning why use it if it produce the same thing in the above 2 code examples? If any one can show me 2 code examples to show how they will give different results I will really appreciate that. I even move the match in the middle but it still gave me the same result as with out using it.

SOURCE

https://www.w3schools.com/jsref/jsref_regexp_begin.asp

Upvotes: 2

Views: 57

Answers (2)

romph
romph

Reputation: 487

\b means a "word-break" character (listed here https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions -> http://www.ecma-international.org/ecma-262/5.1/#sec-15.10.2.6)

var str = "aaaé";
var patt = /\baaa\b/;    
var result = str.match(patt); /* match it */

but 

var str = "aaab";
var patt = /\baaa\b/;    
var result = str.match(patt); /* doesnt match it */

Upvotes: 0

zzxyz
zzxyz

Reputation: 2981

Both of your examples fail to do what the html claims they are going to do. Go to https://www.regextester.com/ and use blahW3blah, W3blah, and blahW3 as your test strings. Your regex should match the last two, but not the first.

You need: (\bW3|W3\b)

(Match W3 at the beginning of a word (\bW3) OR (|) match W3 at the end of a word (W3\b)

Upvotes: 2

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