Question

I have the following code:

    // button sets
    var sets = ['.diamond-colour','.diamond-cut','.diamond-clarity','.diamond-certificate'];
    // for each set
    for (set in sets){
        console.log('Set: '+set);
        console.log(sets[set]);
    }

The console log shows:

Set: 0
.diamond-colour
Set: 1
.diamond-cut
Set: 2
.diamond-clarity
Set: 3
.diamond-certificate
Set: findIndex
function (value){
var ctr = "";
for (var i=0; i < this.length; i++) {
if (this[i] == value) {
return i;
}
}
return ctr;
}

It appears to be a new array element with the key of findIndex and a value being that function.

Would anyone have any idea what this is and why it’s appearing?

Answer 1

You should use a traditional for loop to iterate over an array, otherwise you may pick up properties (in this case a new function) added by yours or 3rd-party code.

for(var i = 0; i < sets.length; i++) {

As others have mentioned, caching the length provides optimal performance:

for(var i = 0, len=sets.length; i < len; i++) {