What\'s the Most Efficient Way to Check if an Item Exists in a JavaScript Array?

Best Way to Find an Item in a JavaScript Array

Determining whether an object exists within an array is a common task in JavaScript. Here are the most efficient ways to achieve this:

1. Array.includes() Method (ES2016)

If you're using a modern browser that supports ECMAScript 2016, the native Array.includes() method is the preferred solution. It takes the item to search for as an argument and returns a boolean indicating its presence.

arr.includes(obj);

2. Array.indexOf() Method

The Array.indexOf() method returns the first index of the searched item if it exists, or -1 if it's not found. To check for existence, you can compare the return value to -1:

function include(arr, obj) {
    return (arr.indexOf(obj) != -1);
}

3. Custom Implementations for Older Browsers

If you need to support older browsers that don't have Array.includes() or Array.indexOf(), you can define your own implementation:

Mozilla's ECMAScript 262 Implementation:

if (!Array.prototype.indexOf) {
    // Add the indexOf method to Array.prototype
}

Daniel James's Implementation:

if (!Array.prototype.indexOf) {
    // Add the indexOf method to Array.prototype
    // with handling for a negative fromIndex
}

roosteronacid's Array.hasObject() Implementation:

Array.prototype.hasObject = function (o) {
    // Add the hasObject method to Array.prototype
    // which returns true if o is found, false if not
};

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