Do JavaScript arrays have an equivalent of Python’s “if a in list”?

Question

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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Answer 1

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

if element not found, you will receive -1

Answered By: Peter Porfy

Answer 2

var IN = function(ls, val){
    return ls.indexOf(val) != -1;
}

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

Answer 3

Since ES6, 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

Answered By: Daniel Kim

Answer 4

The most current way with es6 would be the follow:

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

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

this will return true or false

Answered By: Alex Lytle

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