JavaScript Arrays

JavaScript Array Search

Written by Swapnil RajaPublished 24 Aug 2026

JavaScript indexOf and includes tell you whether a value is in an array and where it sits.

indexOf gives a position, or -1 when the value is missing.

includes gives a simple true or false.

Example

javascript

const fruits = ["Apple", "Banana", "Mango"];

console.log(fruits.indexOf("Banana"));
console.log(fruits.includes("Cherry"));

The output is 1 then false.

Searching an Array

indexOf returns the first matching index, or -1 if there is no match.

includes returns true or false.

Both compare with strict equality, so types must match exactly.

Syntax

javascript

array.indexOf(value);
array.includes(value);

Both take an optional second argument saying where to start.

Checking for -1

Before includes existed, everyone compared against -1.

You will still see this pattern in older code.

Example

javascript

const list = ["a", "b"];

if (list.indexOf("c") === -1) {
  console.log("not found");
}

includes says the same thing far more clearly.

lastIndexOf

This searches from the end and returns the last match.

Example

javascript

const list = ["a", "b", "a"];

console.log(list.indexOf("a"));
console.log(list.lastIndexOf("a"));

The first is 0 and the last is 2.

Strict Comparison

A string and a number are never equal here, even if they look alike.

Example

javascript

const list = [1, 2, 3];

console.log(list.includes(2));
console.log(list.includes("2"));

The second is false, because the types differ.

Searching for Objects

Objects are compared by identity, not by their contents.

Two objects that look the same are still different objects.

Example

javascript

const a = { id: 1 };
const list = [a];

console.log(list.includes(a));
console.log(list.includes({ id: 1 }));

Use find when you need to match on a property.

Starting from a Position

The second argument skips the beginning of the array.

Example

javascript

const list = ["a", "b", "a"];

console.log(list.indexOf("a", 1));

Starting at index 1 finds the later match at index 2.

Complete Example

html

<!DOCTYPE html>
<html>
<head>
  <title>JavaScript Array Search</title>
</head>
<body>

  <h1>JavaScript Array Search</h1>

  <p id="result"></p>

  <script>
    const fruits = ["Apple", "Banana", "Mango"];

    document.getElementById("result").innerHTML =
      "Banana at index " + fruits.indexOf("Banana") +
      "<br>Has Cherry: " + fruits.includes("Cherry");
  </script>

</body>
</html>

Try It Yourself

Run the above example in the Try It Editor.

Try a missing value:

Search for a fruit that is not in the list and see the -1.

Important Points

indexOf returns the first index, or -1 if not found.
includes returns true or false.
lastIndexOf searches from the end.
Both use strict comparison, so types must match.
Objects are matched by identity, not by their contents.

Conclusion

Searching an array is usually a choice between a position and a yes-or-no answer.

includes is clearer whenever you only need to know if something is there.

For matching on a property, the find method is the right tool.

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