How to check whether a string contains a substring in JavaScript?

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52    10 months ago

Usually I would expect a String.contains() method, but there doesn't seem to be one.

What is a reasonable way to check for this?

Answers { 3 }
avatar
10 months ago

Here is a list of current possibilities:

1. (ES6) includesgo to answer (no IE support)

var string = "foo",
    substring = "oo";
string.includes(substring);

2. ES5 and older indexOf

var string = "foo",
    substring = "oo";
string.indexOf(substring) !== -1;

String.prototype.indexOf returns the position of the string in the other string. If not found, it will return -1.

3. searchgo to answer

var string = "foo",
    expr = /oo/;
string.search(expr);

4. lodash includesgo to answer

var string = "foo",
    substring = "oo";
_.includes(string, substring);

5. RegExpgo to answer

var string = "foo",
    expr = /oo/;  // no quotes here
expr.test(string);

6. Matchgo to answer

var string = "foo",
    expr = /oo/;
string.match(expr);

Performance tests are showing that indexOf might be the best choice, if it comes to a point where speed matters.

avatar
10 months ago

You can easily add a contains method to String with this statement:

String.prototype.contains = function(it) { return this.indexOf(it) != -1; };

Note: see the comments below for a valid argument for not using this. My advice: use your own judgement.

Alternatively:

if (typeof String.prototype.contains === 'undefined') { String.prototype.contains = function(it) { return this.indexOf(it) != -1; }; }

avatar
10 months ago

The problem with your code is that JavaScript is case sensitive. Your method call

indexof()

should actually be

indexOf()

Try fixing it and see if that helps:

if (test.indexOf("title") !=-1) {
    alert(elm);
    foundLinks++;
}