Creating a new array of objects from an array in Javascript

Question

So I feel like this should be easy, but I can't figure it out.

To simplify, I need to dynamically generate an array. Then I need my code to build a list of objects based off the middle of that array.

array = [a, b, c, d];
start = array[0];
finish = array[array.length - 1];
middle = [
  { middle: array[1] },
  { middle: array[2] }
]

I need this to be dynamic, so I can't hardcode my middle values due to the array length not being set in stone. I assumed I needed a loop function to iterate through my array, but I've never used this for anything but creating a list in the DOM. I feel like I'm overthinking this or something, because this should be easy... everything I do breaks my code though.

my latest attempt was:

middle = [
  for (i = 1; i < array.length - 2; i++) {
    return { middle: array[i] };
  }
]

I think I get why it doesn't work. It just returns what I want, but I don't think that value ever gets stored.

sjahan · Accepted Answer · 2018-07-10 15:02:32Z

3

Just adjusting @chazsolo's answer to your expected output with a mapping to your target format.

const array = [1,2,3,4,5];
const middle = array.slice(1, -1).map(item => ({middle: item}));
console.log(middle);

answered Jul 10, 2018 at 15:02

sjahan

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2 Comments

chazsolo Over a year ago

Good call, I didn't match his expected output

Dale Spiteri Over a year ago

Man I feel dumb. Ya, just storing that in a variable, and then running that variable where I needed it was all I needed. I was completely overthinking it. Thanks man.

chazsolo · Accepted Answer · 2018-07-10 15:12:27Z

1

Use slice to grab the values you're looking for

const array = [1,2,3,4,5];
const middle = array.slice(1, -1);

console.log(middle);

This returns a new array containing every value except for the first and the last.

If you don't, or can't, use map, then you can still use a for loop:

const array = [1,2,3,4,5];
const middle = array.slice(1, -1);

for (let i = 0; i < middle.length; i++) {
  middle[i] = {
    middle: middle[i]
  };
}

console.log(middle);

edited Jul 10, 2018 at 15:12

answered Jul 10, 2018 at 14:58

chazsolo

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2 Comments

Dale Spiteri Over a year ago

I think the problem with this is I need to format that middle array as an array of objects. I'm not really struggling to get the middle values as much as I'm struggling to reformat the information in a way that the code reads it like the first example.

chazsolo Over a year ago

@sjahan's answer is more complete in that regard. You just need to map each value to your expected format.

Bing Zhao · Accepted Answer · 2018-07-10 15:18:55Z

0

Define an array and push whatever you want to push into it.

let array = ['a', 'b', 'c', 'd']
let middles = []
for (i = 1; i < array.length - 1; i++) {
  middles.push({ middle: array[i] })
}
console.log(middles)

In case you want to learn more, check Array

edited Jul 10, 2018 at 15:18

answered Jul 10, 2018 at 15:13

Bing Zhao

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