Modify RegEx Match in JavaScript

Question

I want to wrap all occurrences of certain words in a given string with square brackets in JavaScript.

Say these words are apples, oranges, and bananas. Then a subject text "You are comparing apples to oranges." should turn into "You are comparing [apples] to [oranges]."

The regular expression for this would be (apples|oranges), but the question is how to wrap or more generally, modify each match. String.replace() lets you replace matches founds with some pre-defined value, rather a value based on the match.

Thanks.

Actually, the regexp for that would be (apples|oranges)... — gnarf
– gnarf, Commented Jan 26, 2011 at 20:04

ThiefMaster · Accepted Answer · 2011-01-26 20:06:23Z

7

js> var str = 'You are comparing apples to oranges.';
js> str.replace(/(apples|oranges)/g, '[$1]')
You are comparing [apples] to [oranges].

If you prefer a function where you can simply feed an array of words:

function reg_quote(str, delimiter) {
    return (str+'').replace(new RegExp('[.\\\\+*?\\[\\^\\]$(){}=!<>|:\\'+(delimiter || '')+'-]', 'g'), '\\$&');
}

function mark_words(str, words) {
    for(var i = 0; i < words.length; i++) {
        words[i] = reg_quote(words[i]);
    }
    return str.replace(new RegExp('(' + words.join('|') + ')', 'g'), '[$1]')
}

Demo:

js> mark_words(str, ['apples', 'oranges']);
You are comparing [apples] to [oranges].
js> mark_words(str, ['apples', 'You', 'oranges']);
[You] are comparing [apples] to [oranges].

If you want it case insensitive, replace 'g' with 'gi'.

answered Jan 26, 2011 at 20:06

ThiefMaster

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Comments

pmdj · Accepted Answer · 2011-01-26 20:10:33Z

6

In addition to the simple substitution string mentioned by others, you can also pass a function to String.replace() which is called for each match, and whose return value is substituted into the resulting string. This lets you do more complicated transformations. For details, see:

https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/String/replace#Specifying_a_function_as_a_parameter

answered Jan 26, 2011 at 20:10

pmdj

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gnarf · Accepted Answer · 2011-01-26 20:05:30Z

3

'You are comparing apples to oranges.'.replace(/(apples|oranges)/g, "[$1]");   
//"You are comparing [apples] to [oranges]."

answered Jan 26, 2011 at 20:05

gnarf

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Comments

Ilya Volodin · Accepted Answer · 2011-01-26 20:13:08Z

1

This is a very ugly code, but it does the job:

    var string = "You are comparing apples to oranges";
    var regEx = "(apples|oranges)";
    var re = new RegExp(regEx, "g");
    for (var i=0; i<string.match(re).length; i++)
    {
        string = string.replace(string.match(re)[i], "[" + string.match(re)[i] + "]");
    }
    alert(string);

answered Jan 26, 2011 at 20:13

Ilya Volodin

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