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JavaScript

Posted by brandonlind2
brandonlind2
7,823 Points

can someone explain why this comparison operator isnt working?

/***the comparison operator in the for loop works perfectly if its < but it stops working
 if I change it to <=, and I cant figure out why***/

function Animal(age, name){ 
    this.age=age; 
    this.name=name; 
    } 
var animals=[
     new Animal(4, 'spike'),
     new Animal(2, 'jack'), 
     new Animal(8, 'Penelope'), 
     new Animal(10, 'speedy')
];

function getIndexNames(arrayName){

    var names=[];

for(var i=0; i <= arrayName.length; i++){
   names.push(arrayName[i].name);
    }

return names;
}

var returnedArr = getIndexNames(animals);

console.log(returnedArr);

1 Answer

Dan Shepherd
Dan Shepherd
4,617 Points

It's because arrays are zero-based.

The last entry in your animals array is 'speedy', at index 3. The length of your array is 4.

When you use the < operator, the for loop will loop over indexes 0,1,2,3 but when you use <=, it will loop over 0,1,2,3,4. There is nothing at index 4 of your array so you get an error when you try access the name property of your non-existing object.

(reposted here because I realised I'd posted in the wrong field)

brandonlind2
brandonlind2
7,823 Points

Thanks!!