callbackFn

A function to execute for each element in the typed array. It should return a truthy value to indicate a matching element has been found, and a falsy value otherwise. The function is called with the following arguments:

element

The current element being processed in the typed array.

index

The index of the current element being processed in the typed array.

array

The typed array findIndex() was called upon.

thisArg Optional

A value to use as this when executing callbackFn. See iterative methods.

The index of the first element in the typed array that passes the test. Otherwise, -1.

See Array.prototype.findIndex() for more details. This method is not generic and can only be called on typed array instances.

The following example finds the index of an element in the typed array that is a prime number (or returns -1 if there is no prime number).

function isPrime(element, index, array) {
  let start = 2;
  while (start <= Math.sqrt(element)) {
    if (element % start++ < 1) {
      return false;
    }
  }
  return element > 1;
}

const uint8 = new Uint8Array([4, 6, 8, 12]);
const uint16 = new Uint16Array([4, 6, 7, 12]);

console.log(uint8.findIndex(isPrime)); // -1, not found
console.log(uint16.findIndex(isPrime)); // 2

• Polyfill of TypedArray.prototype.findIndex in core-js
• JavaScript typed arrays guide
• TypedArray
• TypedArray.prototype.find()
• TypedArray.prototype.findLast()
• TypedArray.prototype.findLastIndex()
• TypedArray.prototype.indexOf()
• TypedArray.prototype.lastIndexOf()
• Array.prototype.findIndex()