JavaScript Foundations Arrays Methods - sorting by length?

Hi Jenny,

Sometimes when it says a previous task is wrong it's usually an error in your current task.

You are correct that the solution is going to involve the .length property.

The sort method is going to take two elements from the array and pass them into the compare function. So a and b will hold the values of two of the strings from the array. It's the length of those strings that we want to compare. So you want to use a.length and b.length.

The compare function is your way of telling the sort method whether a should come before b, or b needs to come before a, or a and b are equal and the order shouldn't change (this is not guaranteed though, they might be reversed).

Here's the long form of the compare function:
copied from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

function compare(a, b) {
  if (a is less than b by some ordering criterion)
     return -1;
  if (a is greater than b by the ordering criterion)
     return 1;
  // a must be equal to b
  return 0;
}

In the first if condition we can see that we should return a negative number if a is less than b. Since we're sorting by lengths here that translates to a.length < b.length So if a is shorter than b we'll return a negative number. This lets the sort method know that it has to keep a before b in the final sorted array.

The second if condition would translate to a.length > b.length

So the final compare function would look like:

saying2.sort(function (a, b) {
  if (a.length < b.length)
     return -1;
  if (a.length > b.length)
     return 1;
  // a must be equal to b
  return 0;
}

So as long as you fill in the correct conditions for the if's this will always work for you.

There is a shorter way to do it though. If you can find a simple expression that duplicates the functionality of the code above then you can use that instead.

LIke this:

saying2.sort(function (a, b) {
  return a.length - b.length;
}

Notice that if a and b have the same length then we'll be returning 0 which is what we want. If a is shorter than b then the expression is going to return some negative number which is exactly what are first if block is doing in the long form. And if a is longer than b then the expression will return some positive number which matches the second if block. So this is functionally equivalent to the longer form.

Ooh. Got it. Thank you! I need to go back and review some JavaScript modules...