question

Question

Javascript Functions
Challenge task 1 of 1
Around line 17, create a function named 'arrayCounter' that takes in a parameter which is an array. The function must return the length of an array passed in or 0 if a 'string', 'number' or 'undefined' value is passed in.
Error:
Bummer! If I pass in an array in to 'arrayCounter' of '1,2,3' I get undefined and not the number 3.
I have been trying to solve this problem for over a week to no avail. Can I please get some help as to what I'm doing wrong?
```Javascript
 function arrayCounter(arr) {
    if (typeof arr === Array) {
      return arr.length;
    }
    else if (typeof arr === 'string' || arr === undefined || !isNaN(arr) ) {
      return 0;
            }
  }
```

Andrew Shook · Accepted Answer

Don, the problem here is that you have run into a JavaScript idiosyncrasy. In JavaScript, typeof array() will return "object" not array, see explanation of typeof (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof). Near the bottom is a code block, look at line 34. In reality the question should be asking you to using Array.isarray();
If you replace the Array in your conditional with 'object' you should be good to go. Also, on a side note, you don't need the else if statement at the bottom of your code. Since the question asks you to only return the length if it is an array, you could just use:
if(something is true){
    return some value;
}else{
    return some other value;
}
or you could do:
if(something){
    return some value;
}
return some other values;

James Barnett · Answer

The easiest way to check if a variable is an array is to see if it's an instance of  the Array constructor.
Use:
if (arr instanceof Array) { }
Instead of:
if (typeof arr === Array) { }

Don Noray · Answer

Thanks a lot! It worked. Thanks for the info on the else if.

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3 Answers

Andrew Shook

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James Barnett

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Don Noray

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Don Noray

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