JavaScript - find indexes of all occurrences of element in array

In this article, we would like to show you how to find indexes of all occurrences of element in array using JavaScript.

Quick solution:

// ONLINE-RUNNER:browser;

function findIndexes(array, value) {
    var indexes = [];
    for (var i = 0; i < array.length; ++i) {
        if (array[i] === value) {
            indexes.push(i);
        }
    }
    return indexes;
}


// Usage example:

var letters = ['a', 'b', 'c', 'b'];
var result = findIndexes(letters, 'b');  // gets indexes of 'b' occurrences

console.log(result);  // [1, 3]

Alternative solution

In this section, we present an alternative solution using Array reduce() method to get indexes of all occurrences of 'b' element in letters array.

// ONLINE-RUNNER:browser;

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

var result = letters.reduce(function(array, value, index) {
    if (value === 'b') {
        array.push(index);
    }
    return array;
}, []);

console.log(result); // [1, 3]

See also

1. JavaScript - get index of item in array

References

1. Array.prototype.reduce() - JavaScript | MDN