what happens behind the scenes when Javascript functions are called

Question

Can someone explain what happens in the below scenario:(this was an interview question)

function test(a){
    alert(a);
}

function test(a,b){
    alert(a,b);
}

function callTest(){
    test(a);
    test(a,b);
}

I was asked how the javascript calls the methods, and what happens behind the scenes in this scenario

Answer 1

If you run it in that order, test(a) will be replaced by test(a,b)

When callTest() is run, then test(a) will alert(a, undefined), then test(a,b) will alert(a,b)

Answer 2

function test(a){     // f1. never called.
    alert(a);
}

function test(a,b){   // f2. overwrite f1 function because name of two functions is same.
    alert(a,b);
}

function callTest(){
    test(1);     // called f2 with (1, undefined)
    test(1,2);   // called f2 with (1, 2)
}
callTest();