JS-059
Educational JavaScript lesson graphic for indexOf(): Learn to find an element's position in an array using indexOf()
Beginner4 min~4 min read#array#indexof#search

indexOf()

Find an element's position

Goal

Learn to find an element's position in an array using indexOf().

Explanation

  • indexOf() searches for a value in an array.
  • If the value is found, its index is returned.
  • If the value is not found, -1 is returned.
  • The method helps determine an element's position.
  • indexOf() is often used together with conditions.

Analogy

You are looking for a book on a shelf and want to know not only whether it is there, but also where it is located.

Code

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

console.log(fruits.indexOf("Banana"));
console.log(fruits.indexOf("Mango"));

Result: 1 -1

Common mistake

Beginners often think -1 means the last element. In fact, it means the element was not found.

Remember

  • ✦ indexOf() returns an element's index.
  • ✦ If the element is absent, it returns -1.
  • ✦ The first element has index 0.

Quick Quiz

What does ["Apple", "Banana"].indexOf("Banana") return?

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