JavaScript Atomics sub() Method

Among the Atomic Operations, there is a method Atomics.sub() that is used to subtract a given value at a given position in the array and return the old value at that position. No other write operation can happen until the modified value is written back.

Syntax:

Atomics.sub(typedArray, index, value)

Parameters:

• typedarray: It is the shared integer typed array you want to modify.
• index: It is the position in the typedArray from where you want to subtract a value from.
• value : It is the number you want to subtract.

Return Value: Atomics.sub() returns the old value at the given position (typedArray[index]). 

Examples of the above function are provided below.

Examples: 

Input : arr[0] = 9;
        Atomics.sub(arr, 0, 3);
Output : 9
 

Input : arr[0] = 3; 
        Atomics.sub(arr, 0, 2);
Output : 3

Examples of the above function are provided below.

Example 1:

javascript

// creating a SharedArrayBuffer
let buf = new SharedArrayBuffer(25);
let arr = new Uint8Array(buf);
// Initialising element at zeroth position of array with 9
arr[0] = 9;

// Displaying the return value of the Atomics.sub() method
console.log(Atomics.sub(arr, 0, 3));

// Displaying the updated SharedArrayBuffer
console.log(Atomics.load(arr, 0));

Output :

9
6

Example 2:

javascript

// creating a SharedArrayBuffer
let buf = new SharedArrayBuffer(25);
let arr = new Uint8Array(buf);

// Initialising element at zeroth position of array with 3
arr[0] = 3;

// Displaying the return value of the Atomics.sub() method
console.log(Atomics.sub(arr, 0, 2));

// Displaying the updated SharedArrayBuffer
console.log(Atomics.load(arr, 0));

Output:

3
1

Application: Whenever we want to update(subtract) a value at a specified position in a given array and want the older value which was at that position to be returned, we use the Atomics.sub() operation in JavaScript.

Example:

javascript

// creating a SharedArrayBuffer
let mybuffer = new SharedArrayBuffer(25);
let myarray = new Uint8Array(mybuffer);

// Initialising the element at zeroth position of array
myarray[0] = 40;

// Displaying the return value of the Atomics.sub() method
console.log(Atomics.sub(myarray, 0, 20));

// Displaying the updated SharedArrayBuffer
console.log(Atomics.load(myarray, 0));

Output :

40
20

Exceptions :

• If the typedArray is not one of the allowed integer types then the Atomics.sub() operation throws a TypeError.
• If the typedArray is not a shared typed array then the Atomics.sub() operation throws a TypeError.
• If the index used as an argument to the Atomics.sub() operation is out of the bound in the typedArray then the Atomics.sub() operation throws a RangeError.

Supported Browser:

• Google Chrome
• Microsoft Edge
• Firefox
• Opera
• Safari

We have a complete list of Javascript Atomic methods, to check those please go through this JavaScript Atomics Complete Reference article.

We have a Cheat Sheet on Javascript where we covered all the important topics of Javascript to check those please go through Javascript Cheat Sheet-A Basic guide to JavaScript.