Record collection challenge again

JavaScript
#1

After many days of pulling my hair out, I apparently solved the challenge with the following:


function updateRecords(id, prop, value) {
 if (value==""){delete collection[id][prop];}
  else if (collection[id].hasOwnProperty("tracks")&&prop=="tracks"){collection[id][prop].push(value)}
  else if (prop=="tracks"){collection[id][prop]=[value]}
  else collection[id][prop]=value;
  return collection;
}

But I am still confused about the solution provided by fCC. They use:


function updateRecords(id, prop, value) {
  if(value === "") delete collection[id][prop];
  else if(prop === "tracks") {
    collection[id][prop] = collection[id][prop] || [ ];
    collection[id][prop].push(value);
  } else {
    collection[id][prop] = value;
  }

  return collection;
}

First, why do they use “===” instead of “==”?

Second, I am confused about the line:

collection[id][prop] = collection[id][prop] || [ ];

I assume this is to handle the cases both where there is already a “tracks” property and where there is not.

I assume that the “collection[id][prop] = collection[id][prop]” part somehow handles the case where there already is a “tracks” property with an array with members (although I don’t know how that works, since fCC hasn’t explained that (ahem!)).

In ordinary language (and I know JS isn’t ordinary language) if someone says “do A or B” that doesn’t tell you what to do. So how does the console know not to set “tracks” to "[]" if there already is an array with members as the value of “tracks”?

#2

I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.

You can also use the “preformatted text” tool in the editor (</>) to add backticks around text.

Pre-formatted-text
Pre-formatted-text1356Ă—380 401 KB

See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (’).

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#3

Thank you! I knew I was doing it wrong and was trying to figure out how to do that. :slight_smile:

#4

=== is strict equality - some says to always use that, and behave as if == doesn’t exist. == will behave weirdly depending on what you need to check

this uses a thing called short-circuit evaluation (in case you want to search it)
a || b is evaluated in this way: first a is evaluated, if it’s truthy, it is what the whole expression evaluates to, if it’s falsy the whole expression evaluates to b
in the use case here, collection[id][prop] can be undefined (falsy) and so the expression is evaluated to the empty array, or an array with values (truthy) and the expression is evaluated to collection[id][prop]

you could do the same with a ternary operator collection[id][prop] = collection[id][prop] ? collection[id][prop] : []
or just with an if statement
if (!collection[id][prop]) {collection[id][prop] = [];}

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#5

Strictly equal (===) is considered the better option than == because it avoids implicit type conversion. Very rarely will you find scenarios where == is appropriate. It will work fine in this challenge, but it’s considered less safe and if you are working on a team you will be asked to change == to === in code reviews.

collection[id][prop] = collection[id][prop] || [ ];

This is just a convenient shorthand (aka “syntactic sugar”) that keeps collection[id][prop] the same if it is truthy or assigns an empty array to collection[id][prop] if it was falsy.

In programming we have a concept called “short circuiting”. For an OR (||) statement, if the as soon as one of the chunks is found to be truthy, it stops checking because the overall evaluation will be true. For an AND (&&) statement it will stop checking as soon as a falsy value is encountered. Both OR and AND evaluate from left to right.

a = true;
b = false;
if (a || b)... // the value of b doesn't matter and is not checked
if (b || a)... // the value of a is checked
if (a && b)... // the value of b is checked
if (b && a)... // the value of a doesn't matter and is not checked.
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#6

Thank you! That’s very helpful. Thank you :smile:

#7

Thank you! That’s very helpful. Yes, I thought it might have something to do with evaluating the expression from left to right. Thank you :smile:

#8

I’m glad I could help. Happy coding!

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