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JavaScript

Posted by Boj H
Boj H
5,021 Points

Question of Challenge task 1 of 1 at Stage 5 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.

My code has problem to check ['string 23'] as an array, please help me out. Thanks.

<script>
  function arrayCounter (a)
  {
    if (typeof a==='undefined') return 0;
    if (!isNaN(a)) return 0; /* number */
    var str_a = a.toString();
    var aa = str_a.split(',');
    console.log(aa);
    console.log(aa.length);
    if (aa.length>1) return a.length;
    else return 0;
  }

  console.log(arrayCounter('string 23'));
  console.log(arrayCounter());
  console.log(arrayCounter(2));
  console.log(arrayCounter('23'));
  console.log(arrayCounter(['1',2,3]));

  console.log(arrayCounter['string 23']);
</script>

5 Answers

Jason Anello
Jason Anello
Courses Plus Student 94,610 Points

Hi Boj,

The way that you're checking if the type is 'undefined' is the same thing you want to do for 'string' and 'number'. You want to use the typeof operator on each one and return 0 if it's any of them. If not, then you can return the length of the array.

function arrayCounter (a)
{
    if (typeof a === 'undefined') {
      return 0;
    }
    if (typeof a === 'string') {
      return 0;
    }
    if (typeof a === 'number') {
      return 0;
    }

    return a.length;
}
pauloliva
pauloliva
7,889 Points
pauloliva
pauloliva
7,889 Points

Is there any way to check that an array it's in fact an array and not an object?

Like when we use typeof(array) it will return as 'object'.

Even when using return array.isArray it will also return the value as an object.

Is there a function that will return 'array' instead of 'object'?

I have checked some answers on stack overflow but they are very confusing.

Like this one:

isArr = Object.prototype.toString.call(data) == '[object Array]';

From where is the 'data' value coming from?

Jason Anello
Jason Anello
Courses Plus Student 94,610 Points

Hi pauloliva ,

Here's the MDN page for isArray: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray

The syntax is Array.isArray(obj). you're calling isArray() on the Array object. Note the capital 'A'

You pass in the thing you're checking and it will return a true or false value depending on whether it was an array or not.

A solution using isArray could look like this:

function arrayCounter (a)
{
    if (Array.isArray(a)) {
      // It's an array, return the length
      return a.length;
    }

    // It wasn't an array, return 0
    return 0;
}
Jason Anello
Jason Anello
Courses Plus Student 94,610 Points

I forgot to answer your question about the code you found.

There's a polyfill on the link I gave you:

if (!Array.isArray) {
  Array.isArray = function(arg) {
    return Object.prototype.toString.call(arg) === '[object Array]';
  };
}

This contains code similar to what you found on stackoverflow.

If you drop that code in first then you will be able to use isArray even if it's not natively available on older browsers.

Binary Soul
Binary Soul
4,592 Points
Binary Soul
Binary Soul
4,592 Points

if (!isNaN(a)) return 0;
Means if 'a' is-not-not-a-number as far as i can see. have you tried:

if (isNaN(a)) return 0;

?

Cody Thompson
PLUS
Cody Thompson
Courses Plus Student 8,430 Points
Cody Thompson
Cody Thompson
Courses Plus Student 8,430 Points

The way I solved the challenge was as following:

 function arrayCounter(a){
        if(typeof a === 'undefined' || typeof a === 'number' || typeof a === 'string' ){
          return 0;
        } else {
          return a.length;
        }
      }

I think you were simply over-thinking the question haha.

pauloliva
pauloliva
7,889 Points
pauloliva
pauloliva
7,889 Points

I did it that way and it gave me errors. :(

Cody Thompson
Cody Thompson
Courses Plus Student 8,430 Points

It shouldn't give you an error if you did it correctly. Read the way you wrote out your initial question;

"return the length of an array passed in OR 0 if a 'string', 'number' OR 'undefined' value is passed in."

"||" = logical OR operator.

Writing it out Jason's way isn't incorrect but in my mind its a bit more semantically correct and less repetitive to use the operator.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_Operators

Take a quick look at that page to read about it.

Jason Anello
Jason Anello
Courses Plus Student 94,610 Points

Hi Cody,

The only reason I didn't use logical OR is because I don't think it was covered up to that point in the course. I try to give solutions that are based on course material and optionally show better solutions.

It does remove the repetition but it's still not the ideal solution.

Arthur Morgan
Arthur Morgan
5,919 Points
Arthur Morgan
Arthur Morgan
5,919 Points

Why does this not work? Maybe I've got the syntax wrong, but what I'm getting at is why the concept doesn't work. Instead of undefined or number or string why not just go for 'not an array'?

 function arrayCounter(a){
        if(typeof a !== 'array'){
          return 0;
        } else {
          return a.length;
        }
      }
Jason Anello
Jason Anello
Courses Plus Student 94,610 Points

Hi Arthur,

This doesn't work because the typeof operator doesn't return the string 'array'

See this mdn page on the typeof operator to see the list of possible strings that it can evaluate to: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof

You can see the solution I posted above using Array.isArray() which is more along the lines of what you are trying to do here.

Tracey Dolby
Tracey Dolby
5,638 Points
Tracey Dolby
Tracey Dolby
5,638 Points

Very confused! Can anyone explain to me why the code needs to be done this way: function arrayCounter (a) { if (Array.isArray(a)) { // It's an array, return the length return a.length; }

// It wasn't an array, return 0
return 0;

or the way that Cody wrote? I don't understand using // (thought this removed phrases from the code) or || (which according to the explanation is the or value, but I don't remember going over this in any videos) I've read through the forum, and my notes from the videos but I still don't remember seeing any code written these ways. An explanation would help me better understand this challenge.

Thanks, Tracey