JavaScript (ES2026) reference · Array Methods

JavaScript Array findIndex() Method

Return the index of the first element that passes a test function, or -1 if none does.

JavaScript (ES2026) Since ES2015

Syntax

array.findIndex(callbackFn, thisArg)

Parameter	Description
`callbackFn`	Called for each element with `(element, index, array)`.

An index, or -1.

First unfinished taskTry it yourself

const tasks = [{ done: true }, { done: false }, { done: false }];
console.log(tasks.findIndex((t) => !t.done));

Output

Check for -1Try it yourself

const list = ["a", "b"];
const i = list.findIndex((x) => x === "z");
console.log(i === -1 ? "not found" : i);

Output

not found

Version	Change
JavaScript ES2015	Added

array.find() · Return the first element that passes a test function, or undefined if none does.
array.indexOf() · Return the first index at which a value is found (using ===), or -1 if it isn't in the array.
array.findLastIndex() · Return the index of the last element that passes a test function, or -1 if none does.
JavaScript Arrays · tutorial
JavaScript Array Methods · tutorial