How to convert an array of key-value tuples into an object

Question

I have an array:

[ [ 'cardType', 'iDEBIT' ],
  [ 'txnAmount', '17.64' ],
  [ 'txnId', '20181' ],
  [ 'txnType', 'Purchase' ],
  [ 'txnDate', '2015/08/13 21:50:04' ],
  [ 'respCode', '0' ],
  [ 'isoCode', '0' ],
  [ 'authCode', '' ],
  [ 'acquirerInvoice', '0' ],
  [ 'message', '' ],
  [ 'isComplete', 'true' ],
  [ 'isTimeout', 'false' ] ]

But I can't access data via an array's key, e.g. arr['txnId'] does not return 20181. How can I convert the above array of tuples into an object, so that I can easily access data by key.

Answer 1

As baao notes, since 2019 you can use Object.fromEntries(arr) (docs) to do exactly this on all modern browsers:

var arr = [['cardType', 'iDEBIT'],
  ['txnAmount', '17.64'],
  ['txnId', '20181']];

console.log(Object.fromEntries(arr));

If that’s not available, my previous solution was to map to an array of key-value objects and combine the objects by spreading into Object.assign:

Object.assign(...arr.map(([key, val]) => ({[key]: val})))

Answer 2

A more idiomatic approach would be to use Array.prototype.reduce:

var arr = [
  [ 'cardType', 'iDEBIT' ],
  [ 'txnAmount', '17.64' ],
  [ 'txnId', '20181' ],
  [ 'txnType', 'Purchase' ],
  [ 'txnDate', '2015/08/13 21:50:04' ],
  [ 'respCode', '0' ],
  [ 'isoCode', '0' ],
  [ 'authCode', '' ],
  [ 'acquirerInvoice', '0' ],
  [ 'message', '' ],
  [ 'isComplete', 'true' ],
  [ 'isTimeout', 'false' ]
];

var obj = arr.reduce(function (o, currentArray) {
  var key = currentArray[0], value = currentArray[1]
  o[key] = value
  return o
}, {})

console.log(obj)
document.write(JSON.stringify(obj).split(',').join(',<br>'))

This is more visually appealing, when done with ES6 (rest parameters) syntax:

let obj = arr.reduce((o, [ key, value ]) => {
    o[key] = value
    return o
}, {})

Answer 3

Use Map.

new Map(array);

The Map object holds key-value pairs and remembers the original insertion order of the keys. Any value (both objects and primitive values) may be used as either a key or a value.

This works because the type of your variable array is Array<[key,value]>. The Map constructor can be initialized with an array of arrays where the first element of the inner arrays is the key and the second is the value.

const array = [
  ['cardType', 'iDEBIT'],
  ['txnAmount', '17.64'],
  ['txnId', '20181'],
  ['txnType', 'Purchase'],
  ['txnDate', '2015/08/13 21:50:04'],
  ['respCode', '0'],
  ['isoCode', '0'],
  ['authCode', ''],
  ['acquirerInvoice', '0'],
  ['message', ''],
  ['isComplete', 'true'],
  ['isTimeout', 'false']
];

const obj = new Map(array);

console.log(obj.get('txnDate'));

Answer 4

arr.reduce((o, [key, value]) => ({...o, [key]: value}), {})

Answer 5

With Object.fromEntries, you can convert from Array to Object:

var entries = [
  ['cardType', 'iDEBIT'],
  ['txnAmount', '17.64'],
  ['txnId', '20181'],
  ['txnType', 'Purchase'],
  ['txnDate', '2015/08/13 21:50:04'],
  ['respCode', '0'],
  ['isoCode', '0'],
  ['authCode', ''],
  ['acquirerInvoice', '0'],
  ['message', ''],
  ['isComplete', 'true'],
  ['isTimeout', 'false']
];
var obj = Object.fromEntries(entries);
console.log(obj);

Answer 6

use the following way to convert the array to an object easily.

var obj = {};
array.forEach(function(e){
   obj[e[0]] = e[1]
})

This will use the first element as the key and the second element as the value for each element.

Answer 7

ES5 Version using .reduce()

const object = array.reduce(function(accumulatingObject, [key, value]) {
  accumulatingObject[key] = value;
  return accumulatingObject;
}, {});

Answer 8

Short ES6 way with Airbnb code style

Exemple:

const obj = arr.reduce((prevObj, [key, value]) => ({ ...prevObj, [key]: value }), {});

Answer 9

The new JS API for this is Object.fromEntries(array of tuples), it works with raw arrays and/or Maps

Answer 10

easiest way to do it where array is of your JSON data :

var obj = {};
array.forEach(function(Data){
obj[Data[0]] = Data[1]
})

Answer 11

I much more recommend you to use ES6 with it's perfect Object.assign() method.

Object.assign({}, ...array.map(([ key, value ]) => ({ [key]: value })));

What happening here - Object.assign() do nothing but take key:value from donating object and puts pair in your result. In this case I'm using ... to split new array to multiply pairs (after map it looks like [{'cardType':'iDEBIT'}, ... ]). So in the end, new {} receives every key:property from each pair from mapped array.

Answer 12

You could do this easily using array reduce in ES6

In this example we create a reducer function and pass an object '{}' as initial value to the reduce function along with the reducer

const arr =    [ [ 'cardType', 'iDEBIT' ],
  [ 'txnAmount', '17.64' ],
  [ 'txnId', '20181' ],
  [ 'txnType', 'Purchase' ],
  [ 'txnDate', '2015/08/13 21:50:04' ],
  [ 'respCode', '0' ],
  [ 'isoCode', '0' ],
  [ 'authCode', '' ],
  [ 'acquirerInvoice', '0' ],
  [ 'message', '' ],
  [ 'isComplete', 'true' ],
  [ 'isTimeout', 'false' ] ];

const reducer = (obj, item) => {
  obj[item[0]] = item[1];
  return obj;
};

const result = arr.reduce(reducer, {});

console.log(result);

Answer 13

let obj ={'abc':123,'other':566};

// first way
let coll= Object.entries(obj).map(i=>Object.assign({'key':i[0],'value':i[1]}))

results: coll => 
0: {key: "abc", value: 123}
1: {key: "other", value: 566}

// second way
let coll2= new Map(Object.entries(obj))
results: coll2 =? 
//[[Entries]]
0: {"abc" => 123}
1: {"other" => 566}