Could someone please explain me this code? This is javascript

Question

var x = [1,2,4,1];
var sum = 0;
for (var i=0 ; i<x.length-1; i++) {
sum+= x[i]
}
document.write(sum);

Answer 1

at first we create an array x. then a variable which will store sum. now we run a loop that will fetch the elements of x the array and add to the sum. so in the loop I is started from 0 it will call x[0] that's the first element and add them next time second and as indexing starts from zero we end it arrays.length - one. and the program prints the sum of all elements of the array expect the last one. to calculate all condition should be x<array.length

Answer 2

It calculate the sum of all elements in the array x but the last element(1).
Output --> 7<---1+2+4