[javascript] How to create dictionary and add key–value pairs dynamically?

From post:

Sending a JSON array to be received as a Dictionary<string,string>

I’m trying to do this same thing as that post. The only issue is that I don’t know what the keys and the values are upfront. So I need to be able to dynamically add the key and value pairs and I don’t know how to do that.

Does anyone know how to create that object and add key value pairs dynamically?

I’ve tried:

var vars = [{key:"key", value:"value"}];
vars[0].key = "newkey";
vars[0].value = "newvalue";

But that doesn’t work.

var dict = {};

dict['key'] = "testing";

console.log(dict);

works just like python :)

console output:

Object {key: "testing"} 

I happened to walk across this question looking for something similar. It gave me enough info to run a test to get the answer I wanted. So if anyone else wants to know how to dynamically add to or lookup a {key: 'value'} pair in a JavaScript object, this test should tell you all you might need to know.

var dictionary = {initialkey: 'initialValue'};
var key = 'something';
var key2 =  'somethingElse';
var value = 'value1';
var value2 = 'value2';
var keyInitial = 'initialkey';

console.log(dictionary[keyInitial]);

dictionary[key] =value;
dictionary[key2] = value2;
console.log(dictionary);

output

initialValue
{ initialkey: 'initialValue',
  something: 'value1',
  somethingElse: 'value2' }

An improvement on var dict = {} is to use var dict = Object.create(null).

This will create an empty object that does not have Object.prototype as it's prototype.

var dict1 = {};
if (dict1["toString"]){
    console.log("Hey, I didn't put that there!")
}
var dict2 = Object.create(null);
if (dict2["toString"]){
    console.log("This line won't run :)")
}

You could create a class Dictionary so you can interact with the Dictionary list easily:

class Dictionary {_x000D_
  constructor() {_x000D_
    this.items = {};_x000D_
  }_x000D_
  has(key) {_x000D_
    return key in this.items;_x000D_
  }_x000D_
  set(key,value) {_x000D_
    this.items[key] = value;_x000D_
  }_x000D_
  delete(key) {_x000D_
    if( this.has(key) ){_x000D_
      delete this.items[key]_x000D_
      return true;_x000D_
    }_x000D_
    return false;_x000D_
  }_x000D_
}_x000D_
_x000D_
var d = new Dictionary();_x000D_
d.set(1, "value1")_x000D_
d.set(2, "value2")_x000D_
d.set(3, "value3")_x000D_
console.log(d.has(2));_x000D_
d.delete(2);_x000D_
console.log(d.has(2));

Its as simple as:

var blah = {}; // make a new dictionary (empty)

or

var blah = {key: value, key2: value2}; // make a new dictionary with two pairs 

then

blah.key3 = value3; // add a new key/value pair
blah.key2; // returns value2
blah['key2']; // also returns value2

In ES6 you can do this:

let cake = '';

let pan = {
  [cake]: '',
};

// Output -> { '': '' }

Old Way

let cake = '';
let pan = {};
pan[cake] = '';

// Output -> { '': '' }

First Initialise Array Globally

var dict = []

Add Object into Dictionary

dict.push(
     { key: "One",value: false},
     { key: "Two",value: false},
     { key: "Three",value: false});

Output : 
   [0: {key: "One", value: false}
    1: {key: "Two", value: false}
    2: {key: "Three", value: false}]

Update Object from Dictionary

Object.keys(dict).map((index) => {        
  if (index == 1){
    dict[index].value = true
  }
});

Output : 
   [0: {key: "One", value: false},
    1: {key: "Two", value: true},
    2: {key: "Three", value: false}]

Delete Object from Dictionary

Object.keys(dict).map((index) => {              
      if (index == 2){
        dict.splice(index)
      }
    });

Output : 
    [0: {key: "One", value: false},
     1: {key: "Two", value: true}]

how about the one liner for creating a key value pair?

let result = { ["foo"]: "some value" };

and some iterator function like reduce to dynamically convert an array to a dictionary

var options = [_x000D_
  { key: "foo", value: 1 },_x000D_
  { key: "bar", value: {id: 2, name: "two"} },_x000D_
  { key: "baz", value: {["active"]: true} },_x000D_
];_x000D_
_x000D_
var result = options.reduce((accumulator, current) => {_x000D_
  accumulator[current.key] = current.value;_x000D_
  return accumulator;_x000D_
}, {});_x000D_
_x000D_
console.log(result);

In case if someone needs to create a dictionary object dynamically you can use the following code snippet

   let vars = [{key:"key", value:"value"},{key:"key2", value:"value2"}];
     let dict={}
     vars.map(varItem=>{
              dict[varItem.key]=varItem.value
            })

    console.log(dict)

var dictionary = {};//create new object
dictionary["key1"] = value1;//set key1
var key1 = dictionary["key1"];//get key1

In modern javascript (ES6/ES2015), one should use Map data structure for dictionary. The Map data structure in ES6 lets you use arbitrary values as keys.

const map = new Map();
map.set("true", 1);
map.set("false", 0);

In you are still using ES5, the correct way to create dictionary is to create object without a prototype in the following way.

var map = Object.create(null);
map["true"]= 1;
map["false"]= 0;

There are many advantages of creating a dictionary without a prototype object. Below blogs are worth reading on this topic.

dict-pattern

objects-as-maps

You can use maps with Map, like this:

var sayings = new Map();
sayings.set('dog', 'woof');
sayings.set('cat', 'meow');

I ran into this problem.. but within a for loop. The top solution did not work (when using variables (and not strings) for the parameters of the push function), and the others did not account for key values based on variables. I was surprised this approach (which is common in php) worked..

  // example dict/json                  
  var iterateDict = {'record_identifier': {'content':'Some content','title':'Title of my Record'},
    'record_identifier_2': {'content':'Some  different content','title':'Title of my another Record'} };

  var array = [];

  // key to reduce the 'record' to
  var reduceKey = 'title';

  for(key in iterateDict)
   // ultra-safe variable checking...
   if(iterateDict[key] !== undefined && iterateDict[key][reduceKey] !== undefined)
    // build element to new array key
     array[key]=iterateDict[key][reduceKey];

JavaScript's Object is in itself like a dictionary. No need to reinvent the wheel.

var dict = {};

// Adding key-value -pairs
dict['key'] = 'value'; // Through indexer
dict.anotherKey = 'anotherValue'; // Through assignment

// Looping through
for (var item in dict) {
  console.log('key:' + item + ' value:' + dict[item]);
  // Output
  // key:key value:value
  // key:anotherKey value:anotherValue
}

// Non existent key
console.log(dict.notExist); // undefined

// Contains key?
if (dict.hasOwnProperty('key')) {
  // Remove item
  delete dict.key;
}

// Looping through
for (var item in dict) {
  console.log('key:' + item + ' value:' + dict[item]);
  // Output
  // key:anotherKey value:anotherValue
}

Fiddle

Since you've stated that you want a dictionary object (and not an array like I assume some understood) I think this is what you are after:

var input = [{key:"key1", value:"value1"},{key:"key2", value:"value2"}];

var result = {};

for(var i = 0; i < input.length; i++)
{
    result[input[i].key] = input[i].value;
}

console.log(result); // Just for testing