Can someone help me interpret these code in words? .... Pls a clear elucidation..

Question

var str = "123"
var res = ""
for(var i = str.length-1;i>= 0;i--){
res+=str[i];
}
document.write(res);

Answer 1

writes the string backwards

Answer 2

This code just copy the initial string but reversed.
The result here is "321".

The reasoning is the following :
str.length-1 = 2;

So we will assign each character of str to res until we get to the 0 index.
So res = str[2]+str[1]+str[0];

You can write the for loop in this way if it help :
for(var i=2; i>=0; i-1)
{
res = res + str[i];
}