LANGUAGE » JAVASCRIPT

Dictionary

Last updated:
Reference:developer.mozilla.org

Basic ​

INFO

Everything in javascript is an Object, but to differentiate these from hash tables, I'll call it dictionary here.

Instantiate:

js
const animal = 'seagull';
const mydict = {
   cat: 'Meow',
   'dog': 'Bark',
   [animal]: 'Mew',
};

Access values (either one is OK):

js
const cat = mydict.cat;
const dog = mydict['dog'];

Delete a key/value pair:

js
delete mydict.cat;

Get number of key/value pairs, can also be used to check if dictionary is empty:

js
const dictLength = Object.keys(mydict).length;

Methods ​

MethodDescription
Object.prototype.hasOwnProperty.call(obj, key)
Object.hasOwn(object, key)		Return true if object owns property, false otherwise.
Object.assign(target, source)Copy all own properties from source to target.
Object.keys(obj)Return an array of keys.
Object.values(obj)Return an array of values.
Object.entries(obj)Return an array of key-value pairs.

Loop key/value pairs ​

js
for (let key in mydict) {
  console.log(`${key}: ${mydict[key]}`);
}

Object.entries(mydict).forEach(([key, value]) => {
  console.log(`${key}: ${value}`);
});

Object.keys(mydict).forEach(function (key) {});

Create a copy ​

js
// Shallow
Object.assign({}, mydict);

// Deep
JSON.parse(JSON.stringify(mydict));

let $ = require('jquery');
$.extend(true, {}, oldDict);

let _ = require('lodash');
_.clonedeep(original);