JavaScript Atomics load() Method

Among the Atomic Operations, there is an inbuilt operation Atomics.load() that is used to return a value that is residing at a given position in an array. The integer typedarray and the index of the value are passed as an argument to the function. Atomics.load() returns the value at the given position of the array.

Note: that Atomics.load() can be used with any of the typed arrays that can be used with shared memory, including Int8Array, Uint8Array, Int16Array, Uint16Array, Int32Array, Uint32Array, Float32Array, and Float64Array. Also, the Atomics.load() method returns the value at the specified index in the typed array.

Syntax:

Atomics.load(typedArray, index)

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 load a value.

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

Examples of the above function are provided below.

Examples: 

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

Input : arr[0] = 3; 
        Atomics.add(arr, 0, 2)
        Atomics.load(arr, 0);
Output : 5

Examples of the above method are provided below.

Example 1:  let’s say we have a SharedArrayBuffer that is being used to share memory between two web workers. We can use the Atomics.load() method to load the value at a specific index in the shared array buffer:

javascript

// create a shared array buffer
const sharedBuffer = new SharedArrayBuffer(4);

// create a view of the shared buffer as a 32-bit integer array
const sharedArray = new Int32Array(sharedBuffer);

// set the value at index 0 to 42
sharedArray[0] = 42;

// load the value at index 0 atomically
const loadedValue = Atomics.load(sharedArray, 0);

console.log(loadedValue); // output: 42

Output:

9

In the above Example 1, we create a SharedArrayBuffer and a view of the buffer as a 32-bit integer array. We set the value at index 0 to 42, and then use Atomics.load() to load the value at index 0 into the loadedValue variable. Because we are using Atomics.load(), the load operation is guaranteed to be atomic with respect to any other agents that have access to the same shared memory.

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 SharedArrayBuffer
console.log(Atomics.load(arr, 0));

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

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

Output :

3
3
5

Application: Whenever we want to return a value from a specified position of an array, we use Atomics.load() 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 SharedArrayBuffer
console.log(Atomics.load(myarray, 0));

Output :

40

Exceptions :

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