Javascript array of objects: Best way to return a value?

Question

I have an array of objects in Javascript with two keys with this structure:

"data": [
  {
  "description": "Unknown",
  "type": 0
  },
  {
  "description": "On",
  "type": 1
  },
  {
  "description": "Off",
  "type": 2
  },
  ...
  ]

I want to pass it a 'type' numeric value and if it finds it in the array, returns me the description value. For example, if I pass '0', I want it to return 'Unknown'.

This is easily done with a for or forEach loop, but there is an inbuilt function in JS that lets me do it in a single line?

[`Array.prototype.find`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find) — Adelin, Jul 09 '18 at 12:08
If you're doing this often, you'll want to flip the data structure to turn it into `{0: 'Unknown', ...}` for fast lookup. — deceze, Jul 09 '18 at 12:10
Possible duplicate of [Find object by id in an array of JavaScript objects](https://stackoverflow.com/questions/7364150/find-object-by-id-in-an-array-of-javascript-objects) — Liam, Jul 09 '18 at 12:11

Nina Scholz · Accepted Answer · 2018-07-09T12:16:09.400

You could use either find

var data = [{ description: "Unknown", type: 0 }, { description: "On", type: 1 }, { description: "Off", type: 2 }];
  
console.log(data.find(({ type }) => type === 1).description);

or for faster access use a hash table for the types

var data = [{ description: "Unknown", type: 0 }, { description: "On", type: 1 }, { description: "Off", type: 2 }], 
    types = Object.assign(...data.map(({ type, description }) => ({ [type]: description })));
  
console.log(types[1]);

or a Map

var data = [{ description: "Unknown", type: 0 }, { description: "On", type: 1 }, { description: "Off", type: 2 }], 
    types = data.reduce((m, { type, description }) => m.set(type, description), new Map);
  
console.log(types.get(1));

@Liam If you have ES6, you can use `map` function. – sametcodes Jul 09 '18 at 12:13 — sametcodes, Jul 09 '18 at 12:13

score 0 · Answer 2 · answered Jul 09 '18 at 12:10

In one liner you can Filter the list.

var obj=[{
  "description": "Unknown",
  "type": 0
  },
  {
  "description": "On",
  "type": 1
  },
  {
  "description": "Off",
  "type": 2
  }];
  var filterType=1;
  console.log(obj.filter(e=>e.type == filterType)[0]['description'])

Chaitanya Babar · Answer 3 · 2018-07-12T06:45:12.670

Have a look at the attached code snippet , which gives the desired output.

Find function to itreat throughout your array to match the condition i.e in this case the passedIndex to check whether it is present in list
If present return the item

var list = [{
    "description": "Unknown",
    "type": 0
  },
  {
    "description": "On",
    "type": 1
  },
  {
    "description": "Off",
    "type": 2
  }
];

function findItem(index) {
  var result = list.find(function(item) {
    if (item.type == index) {
      return item;
    }
  });
  return result.description;
}
var description = findItem(2);
console.log('The Description is "' + description + '"')

.

Javascript array of objects: Best way to return a value?

3 Answers3