Difference between two loops

Question

The code below is the correct, working solution to an exercise I had to work out. I am wondering why my solution did not work.
The only difference I had was this line:
 for (var i = contacts.length; i > 0; i--) {
Why it did not do the same just reversed direction?
for (var i = 0; i < contacts.length; i++) {
    if (contacts[i].firstName == name){
        if (contacts[i].hasOwnProperty(prop)){
            return contacts[i][prop];
        } else{
            return "No such property";
        }
    }
}
return "No such contact";

Khant · Answer

Array Start with 0.
Length Start with 1.
let say i want the last element from contact array
let contact = ['mo','so','do'];
console.log(contact[length])

It won't show a console. Y ? Because To get a last array.
You always need to -1 from the array.length

JMP · Answer

The two loops have different ranges.
If contacts.length had equalled 4, then i would have taken on these values:


console.log('ascending loop');
for (var i = 0; i < 4; i++) {console.log(i);}
console.log('descending loop');
for (var i = 4; i > 0; i--) {console.log(i);}

dahan raz · Answer

There are multiple problems in your code.

the first problem is that you start i = contacts.length and as you know there is no element in the array at the array length position
because arrays go from 0 to array.length-1.
the solution for that problem is var i = contacts.length - 1.
the second problem is that i never goes to zero because your stop condition is i > 0
then you never reach the first element of the array. 
the solution is changing the stop condition to i >= 0

Zinho · Answer

On the answer, the for counter go like 0 ... n, and on your for loop, the counter goes like n ... 1.
So, on your code, the index never is 0

Difference between two loops

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