JavaScript Array indexOf Method (Live Playground)

The indexOf method in JavaScript is used to find the first index at which a given element can be found in the array, or -1 if the element is not found.

Here is a simple example:

let colors = ['blue', 'red', 'green', 'yellow', 'red'];

let index = colors.indexOf('red');

console.log(index);
// Expected output: 1

In this example, indexOf("red") finds the first occurrence of "red" in the colors array and returns its index, which is 1.

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If the element is not found in the array, indexOf returns -1:

let colors = ['blue', 'green', 'yellow'];

let index = colors.indexOf('red');

console.log(index);
// Expected output: -1

In this example, since "red" is not in the colors array, indexOf("red") returns -1.

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You can also specify a second parameter to indicate the index to start the search from:

let colors = ['blue', 'red', 'green', 'yellow', 'red'];

let index = colors.indexOf('red', 2);

console.log(index);
// Expected output: 4

In this example, indexOf("red", 2) starts searching for "red" from index 2. Therefore, it finds the "red" at index 4, not the one at index 1.

Live Playground, Try it Yourself

In conclusion, the indexOf method in JavaScript is a helpful way to find the position of elements in an array. It is a beneficial tool when you need to locate the existence and position of specific items in your array.

Experiment with indexOf on your own to fully understand its usage!