Having trouble understanding this code challenge. Please help...

Hi Richard,

The reason that your if condition isn't working out is because of operator precedence and also how the comma operator works.

The following link contains a table listing operator precedence:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence#Table

You have 3 operators in your condition - typeof, ===, and , From that table we can see that the typeof operator has highest precedence (4), the equality comparison operator === is next highest (9) and the comma , operator has the lowest precedence of all (18).

So the typeof operator has to be evaluated first in the following condition:

if (typeof array === 'string', 'number', 'undefined') {

typeof array will return some string indicating the type of variable it is, let's say 'number'

Now we have:

if ('number' === 'string', 'number', 'undefined') {

The === is evaluated next. 'number' === 'string' will be false since those strings are not equal. However, it could be true if typeof had returned a string type.

Now we have:

if (false, 'number', 'undefined') {

Now the comma operator can finally be evaluated. The way this works is that each comma separated expression is evaluated (if needed) and then the last expression is returned. So this false, 'number', 'undefined' is going to become 'undefined' when it is evaluated because 'undefined' is the last expression.

Now we're down to this:

if ('undefined') {

'undefined' is then converted to a Boolean which becomes true

So you end up with:

if (true) {

This means your function will always return 0 regardless of what you pass into it.

In the code you found, the two pipe characters || are for the logical OR operator. You'll also find that in the table linked above (#14)

You could read this code if (typeof list == "string" || typeof list == "number" || typeof list == "undefined") { in english as "if the type is 'string' OR the type is 'number' OR the type is 'undefined'" So if any of those 3 boolean expressions are true then the whole thing is true and you'll end up returning 0. This may seem more verbose to you than what you were trying to do but it's necessary to make the logic work out right.

Since I don't think this was covered in the course you can also write it out like this:

if (typeof list == "string") {
    return 0;
}
if (typeof list == "number") {
    return 0;
}
if (typeof list == "undefined") {
    return 0;
}

return list.length;

This is more code to write and is repetitive but should be more inline with what you've learned up to this point.

The other questions at the end -

The parameter can be any valid variable name. You used 'array' the other person used 'list'. It's whatever variable name you want to use.

The purpose of the function is to count the number of elements in an array, not how many characters.

Informally, parameters and arguments can be used somewhat interchangeably. More formally, parameters are the variables used as inputs in the function definition whereas arguments are what you pass into the function when you're calling it.

So in your code, array is a parameter for the function.

When you call it like this:

var ages = [34, 59, 18];
arrayCounter(ages);

ages is an argument to the function.

I can't make out what your very last question is asking.