3

I want to know if Javascript RegExp has the ability to turn on and off case insensitivity within the regular expression itself. I know you can set the modifier for the entire regex expression, but that isn't what I'm talking about.

For example, my search string could be:
teXT To seArcH TOP SECRET.

I want to find the insensitive case part "text to search" and then force case sensitivity for "TOP SECRET".

Thus, this wouldn't match (because of case sensitivity for top secret):
teXT To seArcH Top Secret

but this would match (first section case doesn't matter):
text to search TOP SECRET

In Perl, you can do this within the search string. Does Javascript's regular expression engine support anything like this?

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2
  • You could do it with a insensitive regex search followed by a small test. Or by writing some code to make the regex for you. Commented May 24, 2013 at 19:10
  • 1
    No. JavaScript doesn't have scoped modifiers like (?i:...). You pretty much have to do it yourself /[tT][eE][xX][tT] TOP SECRET/, or break your test in two: var m = /text TOP SECRET$/i.match(s); m = m && m[0].match(/TOP_SECRET$/). Commented May 24, 2013 at 19:12

5 Answers 5

Reset to default
4

You can write the RegExp in case-sensitive "longhand"

/[tT][eE][xX][tT] [tT][oO] [sS][eE][aA][rR][cC][hH] TOP SECRET/
    .test('text to search TOP SECRET');
// true

An alternative approach is two regular expressions, an insensitive one followed by a strict one

function test(str) {
    var m = str.match(/text to search (TOP SECRET)/i);
    return (m || false) && /TOP SECRET$/.test(m[1]);
}

test('text to search TOP SECRET'); // true
test('text to search ToP SECRET'); // false

Further, function test above can be optimised in this specific case (as the TOP SECRET part is effectively a string literal which will always have exactly the same form), it doesn't require a second full RegExp test to check it, i.e. you can do

(m || false) && 'TOP SECRET' === m[1];
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Comments

3

What you can do is build your regex like this :

var str = "teXT To seArch";
var r = new RegExp(
  str.split('').map(function(c){return '['+c.toLowerCase()+c.toUpperCase()+']'}).join('')
  + ' TOP SECRET'
);
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1 Comment

+1-ing this as it is the most helpful by way of programmatically creating a RegExp for the desired type of test.
3

According to this reference page, Javascript supports:

No mode modifiers to set matching options within the regular expression.

So the answer is no, you cannot turn case sensitivity on or off within the regular expression.

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Comments

2

Don't think so. I'd suggest doing this:

var m;
var str = "teXT To seArcH TOP SECRET";
if ((m = str.match(/text to search (top secret)/i)) && m[1].match(/TOP SECRET/)) {
  // matched.
}
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Comments

0

Why not simply use 2 Regex's?

var str = "teXT To seArcH TOP SECRET";
if (/text to search/i.test(str) && /TOP SECRET/.test(str)) {
  console.log('match!');
}

I think there is rarely a good reason to make a single very complex regex to cover every case, when you could instead make a handful of Regex's which you combine with code logic. I'd much rather have small bite size Regex's from a maintenance point of view, as figuring what a complex regex actually does can be quite daunting.

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1 Comment

The order of the text is not preserved, not mentioning the case where you want to search for /(?i:text to SEARCH) char/, and the string is tExt to searchar

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