Case-insensitive search

Question

I'm trying to get a case-insensitive search with two strings in JavaScript working.

Normally it would be like this:

var string="Stackoverflow is the BEST";
var result= string.search(/best/i);
alert(result);

The /i flag would be for case-insensitive.

But I need to search for a second string; without the flag it works perfect:

var string="Stackoverflow is the BEST";
var searchstring="best";
var result= string.search(searchstring);
alert(result);

If I add the /i flag to the above example it would search for searchstring and not for what is in the variable "searchstring" (next example not working):

var string="Stackoverflow is the BEST";
var searchstring="best";
var result= string.search(/searchstring/i);
alert(result);

How can I achieve this?

Solution 1

Yeah, use .match, rather than .search. The result from the .match call will return the actual string that was matched itself, but it can still be used as a boolean value.

var string = "Stackoverflow is the BEST";
var result = string.match(/best/i);
// result == 'BEST';

if (result){
    alert('Matched');
}

Using a regular expression like that is probably the tidiest and most obvious way to do that in JavaScript, but bear in mind it is a regular expression, and thus can contain regex metacharacters. If you want to take the string from elsewhere (eg, user input), or if you want to avoid having to escape a lot of metacharacters, then you're probably best using indexOf like this:

matchString = 'best';
// If the match string is coming from user input you could do
// matchString = userInput.toLowerCase() here.

if (string.toLowerCase().indexOf(matchString) != -1){
    alert('Matched');
}

Solution 2

Replace

var result= string.search(/searchstring/i);

with

var result= string.search(new RegExp(searchstring, "i"));

Solution 3

If you're just searching for a string rather than a more complicated regular expression, you can use indexOf() - but remember to lowercase both strings first because indexOf() is case sensitive:

var string="Stackoverflow is the BEST"; 
var searchstring="best";

// lowercase both strings
var lcString=string.toLowerCase();
var lcSearchString=searchstring.toLowerCase();

var result = lcString.indexOf(lcSearchString)>=0;
alert(result);

Or in a single line:

var result = string.toLowerCase().indexOf(searchstring.toLowerCase())>=0;

Solution 4

Suppose we want to find the string variable needle in the string variable haystack. There are three gotchas:

1. Internationalized applications should avoid string.toUpperCase and string.toLowerCase. Use a regular expression which ignores case instead. For example, var needleRegExp = new RegExp(needle, "i"); followed by needleRegExp.test(haystack).
2. In general, you might not know the value of needle. Be careful that needle does not contain any regular expression special characters. Escape these using needle.replace(/[-[\]{}()*+?.,\\^$|#\s]/g, "\\$&");.
3. In other cases, if you want to precisely match needle and haystack, just ignoring case, make sure to add "^" at the start and "$" at the end of your regular expression constructor.

Taking points (1) and (2) into consideration, an example would be:

var haystack = "A. BAIL. Of. Hay.";
var needle = "bail.";
var needleRegExp = new RegExp(needle.replace(/[-[\]{}()*+?.,\\^$|#\s]/g, "\\$&"), "i");
var result = needleRegExp.test(haystack);
alert(result);

Solution 5

ES6+:

let string="Stackoverflow is the BEST";
let searchstring="best";


let found = string.toLowerCase()
                  .includes(searchstring.toLowerCase());

includes() returns true if searchString appears at one or more positions or false otherwise.

View more solutions

Comments

[Dan]

That's a rather messy way around it, as it takes to measures to guard against unexpected regexp metacharacters.

[Sergey Ilinsky]

Dan, I doubt my answer deserves -1 from you. I tried helping ChrisBo by correcting his improper usage of JavaScript, namely: var result= string.search(/searchstring/i); to a proper one, where variable searchstring was used the way he intended.

[glenn jackman]

Dan's right (though he probably meant to say "no measures"): s = 'a[b'; r = new RegExp(s) results in a syntax error (unterminated character class)

[Doug Molineux]

Sorry how can you convert "best" into a variable in your first example? string.match(/best/i);

[Rami]

Why would you use .match for boolean comparison. It searches beyond the first result. You need to stop after first match which .test or .search do. Check performance here.

[Ohad Schneider]

toLowerCase will most likely fail the Turkey Test (moserware.com/2008/02/does-your-code-pass-turkey-test.html) and similar case conversion issues. I'm not sure how ReGex handles it, but if I had to guess I'd say better.

[Medeni Baykal]

@DougMolineux you can use the RegExp object constructor. var text = "best"; var exp = new RegExp(test, "i");. This is same as /best/i.