Replacing using regex in a string javascript

Question

I am trying to replace a particular string using regex.

var replace = {'&lt;RAndom&gt;': "random object"};

I am replacing it using the dynamic regex because i have a lot of objects.

var tagsText = "&lt;RAndom&gt; hellow world";
var regex = new RegExp('\\b(' + Object.keys(replace).join('|') + ')\\b', 'g');
tagsText = tagsText.replace(regex, function(match) {
    return replace[match] + match;
});

But it is not working.I think the problem is with the semicolon but i am not sure.The output is again the same.

"&lt;RAndom&gt; hellow world"

Any ideas?

You should remove the \\bs or replace with (^|\\W) and (\\W|$) respecitively. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Apr 21, 2016 at 10:57

anubhava · Accepted Answer · 2016-04-21 10:59:26Z

2

Problem is presence of \b (word boundary) on each side that is placed before & and ;. Both & and ; are not non-word characters and \b cannot be asserted before and after non-word chars.

You can use \B instead:

var regex = new RegExp('\\B(' + Object.keys(replace).join('|') + ')\\B', 'g');

and then

tagsText  = tagsText.replace(regex, function(match) {
    return replace[match] + match;
});

//=> "random object&lt;RAndom&gt; hellow world"

answered Apr 21, 2016 at 10:59

anubhava

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3 Comments

Wiktor Stribiżew Over a year ago

If a key starts or ends with a word character, this will fail.

anubhava Over a year ago

Right in that case OP's code would have worked. I guess more details needed from OP about the intent behind \b and more examples.

Wiktor Stribiżew Over a year ago

Or use my solution that is context-independent. Kind of :)

Wiktor Stribiżew · Accepted Answer · 2016-04-21 11:03:17Z

1

The word boundary \b and non-word boundary assertion behavior depends on the context. Make it context-independent with unambiguous (^|\W) and ($|\W):

var replace = {'&lt;RAndom&gt;': "random object"};
var tagsText = "&lt;RAndom&gt; hellow world";
var regex = new RegExp('(^|\\W)(' + Object.keys(replace).join('|') + ')(\\W|$)', 'g');
tagsText = tagsText.replace(regex, function(match, g1, g2, g3) {
    return replace[g2] ? replace[g2] + match : match;
});
// And just a demo below
document.body.innerHTML = "<pre>" + tagsText.replace(/&/g, '&amp;') + "</pre>";

The (^|\W) will match the start of string or a non-word character. The ($|\W) will match the end of the string or a non-word character.

Since we have 3 groups now, we can pass them as arguments to the replace callback. With replace[g2] ? replace[g2] + match : match;, we first check if there is a value for g2 key, and if yes, perform the replacement. Else, just return the match.

answered Apr 21, 2016 at 11:03

Wiktor Stribiżew

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1 Comment

soldiershin Over a year ago

Thanks for the awesome explanation :)

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