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JavaScript - TypedArray reduce() Method

The JavaScript TypedArray reduce() method executes the "reducer" callback function provided by the user on each element of the typed array. It returns a single value as a result obtained from executing the callback function over the entire typed array.

It accepts an optional parameter named 'initialValue'. If we do not pass this parameter to the method, it will consider the arr[0] value as the initial value. Additionally, it will execute the callback function on the passed initialValue parameter.

Note − If the current TypedArray is empty or doesn't contain any initial value, this method will throw a 'TypeError' exception.

Syntax

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

reduce(callbackFn, initialValue)

Parameters

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

callbackFn − A user-provided function to execute on each element of the typed array.

This callbackFn function also accepts four parameters, namely 'accumulator', 'currentValue', 'currentIndex', and 'array'. Here's the description for each parameter:

  • accumulator − This parameter represents the accumulated value resulting from previous iterations. It starts with the initial value (either provided explicitly or the first element of the array) and gets updated with each iteration.

  • currentValue − The value of the current element in typed array. If the initialValue is specified, its value will be arr[0], if not it's value will be arr[1].

  • currentIndex − The index position of the currentValue in the typed array.

  • array − The typed array on which the reduce() method gets called.

initialValue − The value to which the accumulator parameter is initialized when the first time the callback function is called.

Return value

This method returns a single value that results from executing the "reducer" callback function to completion over the entire typed array.

Examples

Example 1

The product of all elements within a typed array.

In the following example, we are using the JavaScript TypedArray reduce() method to execute the user-provided function named multi() on each element of this typed array [1, 2, 3, 4, 5]. The multi() function multiplies all the elements within the current typed array. 

<html>
<head>
   <title>JavaScript TypedArray reduce() Method</title>
</head>
<body>
   <script>
      //function
      function multi(accumulator, currentValue){
         return accumulator * currentValue;
      }
      const T_array = new Uint16Array([1, 2, 3, 4, 5]);
      document.write("Typed array: ", T_array);
      
      //using the reduce() method
      document.write("<br>The product of typed array elements: ", T_array.reduce(multi));
   </script>    
</body>
</html>

Output

The above program returns the product of typed array elements as 120.

Typed array: 1,2,3,4,5
The product of typed array elements: 120

Example 2

If we pass the initialValue parameter to this method, the reduce() method also executes the user-provided callback function on it and returns a single value as a result.

In the following example, we use the JavaScript TypedArray reduce() method to execute the user-provided callback function named sum() on each element of the typed array [10, 20, 30, 40, 50], including the passed initialValue parameter value 10. The sum() function accumulates the total sum of all elements within the current typed array.

<html>
<head>
   <title>JavaScript TypedArray reduce() Method</title>
</head>
<body>
   <script>
      const T_array = new Uint16Array([10, 20, 30, 40, 50]);
      document.write("Typed array: ", T_array);
      const initialValue = 10;
      document.write("<br>Initial value: ", initialValue);
      
      let sum = T_array.reduce(function(accumulator, currentValue){
         return accumulator + currentValue;
      }, initialValue);
      document.write("<br>The sum of typed array elements(including initial value): ", sum);
   </script>    
</body>
</html>

Output

After executing the above program, it will return the sum of all elements within the typed array including the initial value −

Typed array: 10,20,30,40,50
Initial value: 10
The sum of typed array elements(including initial value): 160

Example 3

If the current typed array does not contain any element(no initial value available), the reduce() method will throw a "TypeError" exception.

In the given example below, we use the JavaScript TypedArray reduce() method to execute the user-provided reducer callback function named "ArrowFunction" on each element of this empty typed array ([]).

<html>
<head>
   <title>JavaScript TypedArray reduce() Method</title>
</head>
<body>
   <script>
      const T_array = new Uint16Array([]);//empty typed array
      document.write("Length of the typed array: ", T_array.length);
      
      //using the reduce method
      try {
         T_array.reduce((a, b)=> a + b);
      } catch (error) {
         document.write("<br>", error);
      }
   </script>    
</body>
</html>

Output

Once the above program is executed, it will throw a 'TypeError' exception.

Length of the typed array: 0
TypeError: Reduce of empty array with no initial value
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