How do I loop over an array at a given key on an object?

Question

I was given the assignment to create a function that, given an object and a key, returns an array containing all the elements of the array located at the given key that are less than 100. I came up with this:

function getElementsLessThan100AtProperty(obj, key) {
  var lessThan100 = [];
  var targetedKey = obj[key];
  if (targetedKey === undefined) {
    return [];
  }
  for (i = 0; i < targetedKey.length; i++) {
    if (targetedKey[i] < 100) {
      lessThan100.push(targetedKey[i]);
    }
  }
return lessThan100;
}

Now this works, but I am wondering why my original code didn't. I tried to loop over the array at the given property by writing the code below, but it didn't work. Why can't i do this? Also, would someone show me how to clean up this code to make it shorter?

for (i = 0; i <obj[key].length; i++) {
    if (obj[key[i]].length < 100) {
      lessThan100.push(obj[key[i]]);
    }

Jonas Wilms · Accepted Answer · 2018-11-13 21:53:36Z

2

Because obj[key[i]] has to be obj[key][i], additionally you check if the length is smaller 100 which is probably not your intention.

The whole code could be written as:

 const getLessThanHundred = (obj, key) =>
   obj[key].filter(it => it < 100);

answered Nov 13, 2018 at 21:53

Jonas Wilms

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2 Comments

Sheridan Tekosky Over a year ago

Wow. I'm not familiar with that technique yet, but it does work. I am just beginning to learn to code and doing a bootcamp interview training program from hackreactor, so I am still very unfamiliar with javascript. Thank you for the help.

Jonas Wilms Over a year ago

@sheridan glad to help :)

Jonathan · Accepted Answer · 2018-11-13 21:54:21Z

0

In your revised code you are checking if the length of the item in the array is less than 100, not if the value of the item is less than 100. You should be checking the value (ie < 100; not .length < 100)

answered Nov 13, 2018 at 21:54

Jonathan

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3 Comments

Sheridan Tekosky Over a year ago

Wow, thank you so much. Usually, when I make such an obvious mistake, I catch it after spending some time away from the problem and looking at it again with fresh eyes. I've been going back to this problem every day and I didn't catch that.

Sheridan Tekosky Over a year ago

The function is supposed to return an empty array if the property obj[key] does not exist. Do I have to use an if statement for that or is there another way?

Jonathan Over a year ago

You can new up an empty array, and then push items into it if they exist. At the end, return the array. If nothing was added, you will return the empty array that you newed up.

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