23

If I have a list in Python, I can check whether a given value is in it using the in operator:

>>> my_list = ['a', 'b', 'c']

>>> 'a' in my_list
True

>>> 'd' in my_list
False

If I have an array in JavaScript, e.g.

var my_array = ['a', 'b', 'c'];

Can I check whether a value is in it in a similar way to Python’s in operator, or do I need to loop through the array?

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5
  • In other words, I’m asking this question, but for JavaScript instead of Ruby. Commented Sep 16, 2011 at 9:45
  • 2
    possible duplicate: stackoverflow.com/questions/237104/… Commented Sep 16, 2011 at 9:48
  • @6502: ah, that’s the stuff. Write that up into an answer and the points are yours. Commented Sep 16, 2011 at 9:48
  • Check this qeustion. Commented Sep 16, 2011 at 9:49
  • @mouad: great spot — I’m actually using underscore.js, which the top answer to that question mentions, so I might use their function for this. Commented Sep 16, 2011 at 9:49

4 Answers 4

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31

Since ES7, it is recommended to use includes() instead of the clunky indexOf().

var my_array = ['a', 'b', 'c'];

my_array.includes('a');  // true

my_array.includes('dd'); // false
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15 
var my_array = ['a', 'b', 'c'];
alert(my_array.indexOf('b'));
alert(my_array.indexOf('dd'));

if element not found, you will receive -1

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3 Comments

In modern browser, yes, but older internet explorers does not support it. Here is a question about it (and the workaround): stackoverflow.com/questions/2790001/…
what if searched item exists more than one in an array ?
@Ciastopiekarz indexOf returns the first occurrence: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…
3 
var IN = function(ls, val){
    return ls.indexOf(val) != -1;
}

var my_array = ['a', 'b', 'c'];
IN(my_array, 'a');
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1

The most current way with ES7 would be the following:

let myArray = ['a', 'b', 'c'];

console.log(myArray.includes('a'))

This will return true or false.

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