Destructing assignment to swap the values in ES6

I am revising JavaScript and came to following ES6 example.

let a = 8, b = 6;
// change code below this line
[a,b] = [b,a];
// change code above this line
console.log(a); // a is 6
console.log(b); // b is 8

Not able to figure out how this is working, as we have assignment operator with both side arrays.