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JavaScript JavaScript Foundations Functions Return Values

Challenge 1 of Return Values

"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".

Can anyone shed any light onto this challenge? I am totally stuck.

2 Answers

The challenge is a little strange because 'typeof' is discussed in the video but that isn't the best way to determine what is or isn't an array.

The code I wrote which worked is:

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

As you can see, it works even though there are non-array objects that the function will still try to return a length for.

Better code posted by Dave McFarland uses 'instanceof Array' to determine what is or isn't an array but 'instanceof' isn't mentioned anywhere in the video:

function arrayCounter (array) {
    if (array instanceof Array) {
        return array.length;
    } else {
        return 0;
var myArray = [1,2,3];
console.log(arrayCounter(myArray)); // prints 3 to the console
var myString = 'test';
console.log(arrayCounter(myString)); // prints 0 to the console
var myObj = { name: 'object' };
console.log(arrayCounter(myObj)); // prints 0 to the console

Thank you for your answer! Much appreciated.