Why console.log(a) doesn't return same result [1, 2, 3, 4] as console.log(b) ?
function test(c, d) {
c = [1, 2, 3, 4];
d.push(4);
}
a = [1, 2, 3];
b = [1, 2, 3];
test(a, b);
console.log(a);
console.log(b);
With a = [1, 2, 3, 4]; you are overriding the argument (which is local to the function) you have passed into the function test. You are not making any changes to the actual array a.
Now the a inside does not even point to the array a outside.
But there is a change happening when you do b.push(4), which actually mutates the b array outside.
function test(a, b) {
a = [1, 2, 3, 4];
b.push(4);
}
a = [1, 2, 3];
b = [1, 2, 3];
test(a, b);
console.log(a);
console.log(b);