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JavaScript JavaScript Foundations Functions Return Values

Posted by Anthony Williams
Anthony Williams
10,813 Points

JavaScript Functions first code challenge

I am trying to determine if the array name itself is being looked at as a the variable name or the contents of the array. If it is being looked at as the contents of the array, how do you check if the functions input is a string, number, or undefined without looking at the contents within the array?

link to the code challenge: http://teamtreehouse.com/library/return-values

function arrayCounter(a){
 if (typeof a === "string", 4, 'undefined'){
 return 0;}
 return a.length;
}         
```   ???
If possible, please explain. Thanks : )

3 Answers

notf0und
notf0und
11,940 Points

You'll need separate "typeof" checks for each type.

if (typeof a === "string" || typeof a === "number" || typeof a === "undefined")

Should work. If any of those are true, that will return 0. Otherwise, return the length of the array.

Anthony Williams
Anthony Williams
10,813 Points

Thank you Bryan. Very helpful!!

Michael Miller
Michael Miller
5,747 Points
Michael Miller
Michael Miller
5,747 Points

I believe the best answer is to use the instanceof operator. For example:

if(array instanceof Array){
    return array.length;
}else{
    return 0;
}

This will return 0 for anything other than an array, and return array.length if it is an array.

Anthony Williams
Anthony Williams
10,813 Points

Thanks Mike. Crazy how many ways you can solve a problem. I did notice with the "typeof" operator it recognizes the array as "object". "Array" is a key word in JS right? so when declared with "instanceof" it can differentiate between different object types?

Jeff Lange
Jeff Lange
8,788 Points
Jeff Lange
Jeff Lange
8,788 Points

Excellent solution! Unfortunately, if you're expecting to be able to solve the challenge only with what you've been taught in the preceding videos (like myself), then you feel dismayed that they never taught you the "instanceof" method.

Michael Miller
Michael Miller
5,747 Points
Michael Miller
Michael Miller
5,747 Points

Good questions Anthony. I had to look this up, but I believe the best answer to your original question is to use Array.isArray(object). The typeof operator can only return one of seven types (undefined, number, string, boolean, symbol, function, object). It cannot return what type of object it is, only whether it is or isn't one. My original suggestion, instanceof, will work most of the time since it checks to see if the object compared is in it's prototype chain. In other words is myArray an instance of the Array object. From what I've read there are some loopholes which could make instanceof return a bad result. (Don't ask me to explain them I don't really understand what they were saying). Array.isArray() is supposed to be a bullet proof way of testing whether an object is an array or not. I hope this all makes sense.

If you're interested check out these articles:

Determining with absolute accuracy whether or not a JavaScript object is an array

Array.isArray()

instanceof

typeof

Jeff Lange
Jeff Lange
8,788 Points
Jeff Lange
Jeff Lange
8,788 Points

Good answer again!

I wish they had taught us the stuff in the videos they are expecting us to be able to solve...sheesh. :D

Michael Miller
Michael Miller
5,747 Points

Agreed. I think instanceof was very briefly mentioned, but I think they should teach us how and where to look for more information when we're stuck.