JavaScript case insensitive string comparison

JavaScript case insensitive string comparison

How do I perform case insensitive string comparison in JavaScript?

Solutions/Answers:

Solution 1:

The simplest way to do it (if you’re not worried about special Unicode characters) is to call toUpperCase:

var areEqual = string1.toUpperCase() === string2.toUpperCase();

Solution 2:

EDIT: This answer was originally added 9 years ago. Today you should use localeCompare with the sensitivity: 'accent' option:

function ciEquals(a, b) {
    return typeof a === 'string' && typeof b === 'string'
        ? a.localeCompare(b, undefined, { sensitivity: 'accent' }) === 0
        : a === b;
}

console.log("'a' = 'a'?", ciEquals('a', 'a'));
console.log("'AaA' = 'aAa'?", ciEquals('AaA', 'aAa'));
console.log("'a' = 'á'?", ciEquals('a', 'á'));
console.log("'a' = 'b'?", ciEquals('a', 'b'));

The { sensitivity: 'accent' } tells localeCompare() to treat two variants of the same base letter as the same unless they have different accents (as in the third example) above.

Alternatively, you can use { sensitivity: 'base' }, which treats two characters as equivalent as long as their base character is the same (so A would be treated as equivalent to á).

Note that the third parameter of localeCompare is not supported in IE10 or lower or certain mobile browsers (see the compatibility chart on the page linked above), so if you need to support those browsers, you’ll need some kind of fallback:

function ciEqualsInner(a, b) {
    return a.localeCompare(b, undefined, { sensitivity: 'accent' }) === 0;
}

function ciEquals(a, b) {
    if (typeof a !== 'string' || typeof b !== 'string') {
        return a === b;
    }

    //      v--- feature detection
    return ciEqualsInner('A', 'a')
        ? ciEqualsInner(a, b)
        : /*  fallback approach here  */;
}

Original answer

The best way to do a case insensitive comparison in JavaScript is to use RegExp match() method with the i flag.

Case-insensitive search

When both strings being compared are variables (not constants), then it’s a little more complicated ’cause you need to generate a RegExp from the string but passing the string to RegExp constructor can result in incorrect matches or failed matches if the string has special regex characters in it.

If you care about internationalization don’t use toLowerCase() or toUpperCase() as it doesn’t provide accurate case-insensitive comparisons in all languages.

http://www.i18nguy.com/unicode/turkish-i18n.html

Solution 3:

With the help of regular expression also we can achieve.

(/keyword/i).test(source)

/i is for ignore case. If not necessary we can ignore and test for NOT case sensitive match like

(/keyword/).test(source)

Solution 4:

Remember that casing is a locale specific operation. Depending on scenario you may want to take that in to account. For example, if you are comparing names of two people you may want to consider locale but if you are comparing machine generated values such as UUID then you might not. This why I use following function in my utils library (note that type checking is not included for performance reason).

function compareStrings (string1, string2, ignoreCase, useLocale) {
    if (ignoreCase) {
        if (useLocale) {
            string1 = string1.toLocaleLowerCase();
            string2 = string2.toLocaleLowerCase();
        }
        else {
            string1 = string1.toLowerCase();
            string2 = string2.toLowerCase();
        }
    }

    return string1 === string2;
}

Solution 5:

As said in recent comments, string::localCompare supports case insensitive comparisons (among other powerful things).

Here’s a simple example

'xyz'.localeCompare('XyZ', undefined, { sensitivity: 'base' }); // returns 0

And a generic function you could use

function equalsIgnoringCase(text, other) {
    text.localeCompare(other, undefined, { sensitivity: 'base' }) === 0;
}

Note that instead of undefined you should probably enter the specific locale you are working with. This is important as denoted in the MDN docs

in Swedish, ä and a are separate base letters

Sensitivity options

Sensitivity options tabulated from MDN

Browser support

As of time of posting, UC Browser for Android and Opera Mini do not support locale and options parameters. Please check https://caniuse.com/#search=localeCompare for up to date info.

Solution 6:

if you are concerned about the direction of the inequality (perhaps you want to sort a list)
you pretty-much have to do case-conversion, and as there are more lowercase characters in unicode than uppercase toLowerCase is probably the best conversion to use.

function my_strcasecmp( a, b ) 
{
    if((a+'').toLowerCase() > (b+'').toLowerCase()) return 1  
    if((a+'').toLowerCase() < (b+'').toLowerCase()) return -1
    return 0
}

Javascript seems to use locale “C” for string comparisons so the resulting ordering will
be ugly if the strings contain other than ASCII letters. there’s not much that can be done about that without doing much more detailed inspection of the strings.