How to iterate (keys, values) in javascript?

How to iterate (keys, values) in javascript?

I have a dictionary that has the format of
dictionary = {0: {object}, 1:{object}, 2:{object}}

How can I iterate through this dictionary by doing something like
for((key,value) in dictionary){
//Do stuff where key would be 0 and value would be the object
}

Solutions/Answers:

Solution 1:

tl;dr

  1. In ECMAScript 5, it is not possible.
  2. In ECMAScript 2015, it is possible with Maps.
  3. In ECMAScript 2017, it would be readily available.

ECMAScript 5:

No, its not possible with objects.

You should either iterate with for..in, or Object.keys, like this

for (var key in dictionary) {
    // check if the property/key is defined in the object itself, not in parent
    if (dictionary.hasOwnProperty(key)) {           
        console.log(key, dictionary[key]);
    }
}

Note: The if condition above is necessary, only if you want to iterate the properties which are dictionary object’s very own. Because for..in will iterate through all the inherited enumerable properties.

Or

Object.keys(dictionary).forEach(function(key) {
    console.log(key, dictionary[key]);
});

ECMAScript 2015

In ECMAScript 2015, you can use Map objects and iterate them with Map.prototype.entries. Quoting example from that page,

var myMap = new Map();
myMap.set("0", "foo");
myMap.set(1, "bar");
myMap.set({}, "baz");

var mapIter = myMap.entries();

console.log(mapIter.next().value); // ["0", "foo"]
console.log(mapIter.next().value); // [1, "bar"]
console.log(mapIter.next().value); // [Object, "baz"]

Or iterate with for..of, like this

'use strict';

var myMap = new Map();
myMap.set("0", "foo");
myMap.set(1, "bar");
myMap.set({}, "baz");

for (const entry of myMap.entries()) {
  console.log(entry);
}

Output

[ '0', 'foo' ]
[ 1, 'bar' ]
[ {}, 'baz' ]

Or

for (const [key, value] of myMap.entries()) {
  console.log(key, value);
}

Output

0 foo
1 bar
{} baz

ECMAScript 2017

ECMAScript 2017 would introduce a new function Object.entries. You can use this to iterate the object as you wanted.

'use strict';

const object = {'a': 1, 'b': 2, 'c' : 3};
for (const [key, value] of Object.entries(object)) {
  console.log(key, value);
}

Output

a 1
b 2
c 3

Solution 2:

Try this:

dict = {0:{1:'a'}, 1:{2:'b'}, 2:{3:'c'}}
for (var key in dict){
  console.log( key, dict[key] );
}

0 Object { 1="a"}
1 Object { 2="b"}
2 Object { 3="c"}

Solution 3:

The Object.entries() method has been specified in ES2017 (and is supported in all modern browsers):

for (const [ key, value ] of Object.entries(dictionary)) {
    // do something with `key` and `value`
}

Explanation:

  • Object.entries() takes an object like { a: 1, b: 2, c: 3 } and turns it into an array of key-value pairs: [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', 3 ] ].

  • With for ... of we can loop over every entry of the so created array.

  • Since we are guaranteed that each of the so iterated array items is another two-entry-array, we can use destructuring to directly assign variables key and value to its first and second item.

Related:  Detect Search Crawlers via JavaScript

Solution 4:

You can do something like this :

dictionary = {'ab': {object}, 'cd':{object}, 'ef':{object}}
var keys = Object.keys(dictionary);

for(var i = 0; i < keys.length;i++){
   //keys[i] for key
   //dictionary[keys[i]] for the value
}

Solution 5:

Try this:

var value;
for (var key in dictionary) {
    value = dictionary[key];
    // your code here...
}

Solution 6:

I think the fast and easy way is

Object.entries(event).forEach(k => {
    console.log("properties ... ", k[0], k[1]); });

just check the documentation
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/entries