Atomics static method sub() in Javascript

The Atomics static method sub() used to perform subtraction operation with a given value at a given position in the array. It returns the old value at that position. It guarantees that no other write happens until the modified value is written on shared object.

Syntax

 1 Atomics.sub(<typedArray>, <index>, <value>)

typeArray : A typed array object to subtract specified value, It can be of type Int8Array, Uint8Array, Int16Array, Uint16Array, Int32Array, Uint32Array, BigInt64Array, or BigUint64Array.

index : An index value which specify the position

value : A value to subtract from the specified index position

Static method sub()

 1 const shared= new SharedArrayBuffer(1024);
 2 const ua = new Uint8Array(shared);
 3 
 4 ua[0] = 100;
 5 
 6 console.log("An initial value is :", ua[0]);
 7 // returns an old value which is 100
 8 let res1 = Atomics.sub(ua, 0, 50); 
 9 console.log("A previous value is :", res1);
 10 
 11 // returns an old value which is 50
 12 let res2 = Atomics.sub(ua, 0, 10);
 13 console.log("A previous value is :", res2)
 14 
 15 let res3 = Atomics.load(ua, 0); // returns 40
 16 console.log("A resulting value is :", res3);

In the above example, A Uint8Array is created by specifying shared buffer array object. A new value assign at position 0. A sub() method called by specifying index 0 and 50 which subtracted and returns old value 100. Again, a sub() method called by specifying index 0 and 10 which subtract and old value 50 returns. A load() method called which returns index 0 value and prints 40 on console.

Output

 1 An initial value is : 100
 2 A previous value is : 100
 3 A previous value is : 50
 4 A resulting value is : 40

Subtract value dynamically

 1 let values = [3, 5, 8, 9, 5];
 2 
 3 const shared= new SharedArrayBuffer(1024);
 4 const ua = new Int8Array(shared);
 5 ua[0] = 60;
 6 
 7 console.log("Initial value :", ua[0]);
 8 values.forEach(val => {
 9     let x = Atomics.sub(ua, 0, val);
 10     console.log("A previous value is :", x);
 11 });
 12 let res = Atomics.load(ua, 0);
 13 console.log("Result after subtraction :", res);

In the above example, an array is declared and initialized with values. An array elements are iterating using forEach() method by specifying a callback function. A callback function subtract element value by calling an Atomics sub() method and returns a previous value and print. A initial and resulting value print by accessing an element 0 using Atomics load() method.

Output

 1 Initial value : 60
 2 A previous value is : 60
 3 A previous value is : 57
 4 A previous value is : 52
 5 A previous value is : 44
 6 A previous value is : 35
 7 Result after subtraction : 30