Could someone ELI5 returning object array values from this code example?

Question

Hello All^^ I apologize for the simplicity of this question (and my JS comprehension), beforehand. Could someone explain why the following code returns the key value in the object array? I would expect that array-name[n] would return the key, rather than the value in the array. I thought that array-name[n][1] would produce the value (name of the shape in this example) in this function ( i.e., if 4 is entered, "square" would be returned). For the background, this was an edabit challenge that I solved. However, that was not entirely on purpose(I was initially trying to use a loop to perform the same function for about a half hour, to no avail). To digress, I would simply like to understand this more thoroughly, if possible. I appreciate your time.

    const polygons = {
     1 :  "circle" ,
     2 :  "semi-circle",
     3 :  "triangle",
     4 :  "square",
     5 :  "pentagon",
     6 :  "hexagon",
     7 :  "heptagon",
     8 :  "octagon",
     9 :  "nonagon",
     10 : "decagon"
};
return polygons[n];
}

Because that's how objects (polygons isn't an array here) work. If you want the keys use let keys = Object.keys(polygons); — JDunken
– JDunken, Commented Feb 5, 2020 at 20:50
Yes, n is always a number between 1 and 10^^ Sry for leaving that bit out. — UselessGiraffe
– UselessGiraffe, Commented Feb 5, 2020 at 20:50

Ashish Modi · Accepted Answer · 2020-02-05 21:02:42Z

4

Your polygon is an object. It is not an array hence you are seeing this behavior. See code below for better explanation.

// This is object. Doing polygons[4] will give you square
const polygons = {
  1 :  "circle" ,
  2 :  "semi-circle",
  3 :  "triangle",
  4 :  "square",
  5 :  "pentagon",
  6 :  "hexagon",
  7 :  "heptagon",
  8 :  "octagon",
  9 :  "nonagon",
  10 : "decagon"
};

function getFromObject(n) {
  return polygons[n];
}

// This is array. Doing polygons[4] will give you pentagon (because array index start from 0)
const polygons = [
  "circle" ,
  "semi-circle",
  "triangle",
  "square",
  "pentagon",
  "hexagon",
  "heptagon",
  "octagon",
  "nonagon",
  "decagon"
];

function getFromArray(n) {
  return polygons[n];
}

If you need keys from your object, you could do Object.keys(polygons). This return you array of keys. I am not sure what your usecase is but this how it works.

answered Feb 5, 2020 at 21:02

Ashish Modi

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3 Comments

UselessGiraffe Over a year ago

Thanks for the explanation. I thought that this was called an "object array", rather than a regular array. However, my coding verbiage understanding is poor. So 1 : "circle" is simply one value of the object? They are still key and values, are they not? If I am mistaken (which is likely the case), then what would 1 and "circle" be called, respectively? Please let me know.

Evan Bechtol Over a year ago

1: "circle" is a key/value pair in the object polygons. 1 is the key which corresponds to the value "circle". Together, they create a key/value pair, which is unique; you cannot have 2 identical keys in an object. MDN Object Docs is a great resource to learn more!

UselessGiraffe Over a year ago

Thank you for the explanation. That makes sense and confirms my understanding of key/values. I suppose, what was confusing to me was why object[n] grabs only the value. I thought that a one bracketed number argument would translate to the key position (rather than the value position). Anyway, thanks again^^ Really appreciate it.

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