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Beat Mix: Why does one function use let where another use const?

#1

Hey all,

So I was completely lost and decided to look at the solution to the Beat Mix Project (Project 2). I realize now it’s better to come to the forum and look for help but there was no Beat Mix posts and I had no specific questions to ask aside from “Where do I even begin??”.

Anyways, in the solution for presentHandler.js is the following code:

const presetHandler = (method, index, newPresetArray) => {
  if (method === 'GET') {
    let preset = getPreset(index);
    if (preset) {
      return [200, preset];
    } else {
      return [404];
    }
  } else if (method === 'PUT') {
    const newPreset = createOrUpdatePreset(index, newPresetArray);
    if (newPreset) {
      return [200, newPreset];
    } else {
      return [404];
    }
  } else {
    return [400];
  }
};

I’m confused why the GET method requires a let function whereas the PUT method uses const? They seem to be almost identical? Any help would be much appreciated. Thanks!

#2

One line of thinking suggests that if the intention is to update a variable at some point, then use let, otherwise use const. In the code above preset and newPreset are never changed so const is fine to use. In such a simple function, it makes no difference which keyword we use. I tend to use let inside functions, and const to define global constants.

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#3

mtf - I see you alot in these forums! Thank you so much for the reply! I will keep this in mind as I write and study more code.

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#4 
function ...
    const x ...
    for let i ...
    ...
    for let i ...
    ...

In this sense, x is a global to the two loop bodies. i is local only to the loop it exists in and not visible in that (or any) global scope.

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