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JavaScript - TypedArray findIndex() Method

The JavaScript TypeArray findIndex() method returns an index of the first element in the current typed array that satisfies the provided testing function. If no values are satisfied or no value is passed to the testing function, -1 is returned.

Here's the some additional points about findIndex() method −

  • The findIndex() method operates on a TypedArray (such as Uint8Array, Int16Array, etc.).

  • It accepts a testing function as a parameter.

  • The testing function is executed for each element in the TypedArray.

  • If an element satisfies the condition specified by the testing function (returns a true value), an index of the element is returned as the result.

  • If no elements are passed to the testing function, −1 is returned.

Syntax

Following is the syntax of JavaScript TypedArray findIndex() method −

findIndex(callbackFn, thisArg)

Parameters

This method accepts two parameters named 'callbackFn' and 'thisArg', which are described below −

callbackFn − This parameter is a testing function that will be executed for each element in the TypedArray.

This function takes three parameters named 'element', 'index', and 'array'. Here's the description for each parameter −

  • element − Represents the current element being processed in the TypedArray.

  • index − Indicates the index (position) of the current element within the TypedArray.

  • array − Refers to the entire TypedArray.

thisArg (optional) − This is an optional parameter that allows you to specify the value of this within the callbackFn.

Return value

This method returns an index of the first element in typed array that satisfied the provided test function, '−1' otherwise.

Examples

Example 1

In the following example, we use the JavaScript TypedArray findIndex() method to search for the index of the first even number in the original TypedArray [1, 2, 3, 4, 5, 6, 7, 8]. We create a testing function named isEven() that checks if a number is even, and then pass this function as an argument to the findIndex() method.

<html>
<head>
   <title>JavaScript TypedArray findIndex() Method</title>
</head>
<body>
   <script>
      function isEven(element, index, array){
         return element %2 == 0;
      }
      const T_array = new Int8Array([1, 2, 3, 4, 5, 6, 7, 8]);
      document.write("Orizinal TypedArray: ", T_array);
      document.write("<br>An index of the first even number in TypedArray is: ");
      document.write(T_array.findIndex(isEven));
   </script>    
</body>
</html>

Output

The above program returns an index of the first even number as '1' in the typed array [1, 2, 3, ,4 ,5 ,6 ,7, 8].

Orizinal TypedArray: 1,2,3,4,5,6,7,8
An index of the first even number in TypedArray is: 1

Example 2

The following is another example of the JavaScript TypedArray findIndex(). In this example, we use the JavaScript TypedArray findIndex() method to search for an index of the first negative number in the TypedArray [1, 2, −1, 0, 1, 2, −2, −3]. We create a testing function that checks if a number is negative and then pass this function as an argument to the findIndex() method.

<html>
<head>
   <title>JavaScript TypedArray findIndex() Method</title>
</head>
<body>
   <script>
      function isNegative(element, index, array){
         return element < 0;
      }
      const T_array = new Int8Array([1, 2, -1, 0, 1, 2, -2, -3]);
      document.write("Orizinal TypedArray: ", T_array);
      document.write("<br>An index of the first negative number in TypedArray is: ");
      document.write(T_array.findIndex(isNegative));
   </script>    
</body>
</html>

Output

After executing the above program, it returns an index of the first negative number as 2 in the typed array [1, 2, −1, 0, 1, 2, −2, −3].

Orizinal TypedArray: 1,2,-1,0,1,2,-2,-3
An index of the first negative number in TypedArray is: 2

Example 3

If no value satisfies the testing function, it will return '−1'.

In this program, we create a function called isPrime() that checks whether a number is prime. We use this function as an argument to the findIndex() function to retrieve an index of the first prime number in the TypedArray [4, 6, 8, 9]. However, since no value satisfies the isPrime() function, the findIndex() method returns −1.

<html>
<head>
   <title>JavaScript TypedArray findIndex() Method</title>
</head>
<body>
   <script>
      function isPrime(element, index, array){
         let begin = 2;
         while(begin <= Math.sqrt(element)){
            if(element % begin++ < 1){
               return false;
            }
         }
         return element > 1;
      }
      const T_array = new Int8Array([4, 6, 8, 9]);
      document.write("Orizinal TypedArray: ", T_array);
      document.write("<br>First negative number in TypedArray is: ");
      document.write(T_array.findIndex(isPrime));
   </script>    
</body>
</html>

Output

Once the above program is executed, it will return -1.

Orizinal TypedArray: 4,6,8,9
First negative number in TypedArray is: -1

FindIndex() vs Find() Method

Both the findIndex() and find() methods are similar to each other, but there are few differences are listed below −

  • The findIndex() and find() methods on typed arrays are very similar. The findIndex() returns the index where the first element is located in the typed array, whereas the find() method returns the first element itself.

  • If no value is satisfied or no element is passed to the findIndex() method, it returns −1, whereas the find() method returns 'undefined'.

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