From the perspective of someone who has a primer on Ruby and jumping onto JavaScript, I noticed something used very often in Ruby that is missing from JavaScript: Ruby Hashes. How can such a powerful data type not exist in other object-oriented languages? If you are also completely new to JavaScript and have the same question, fear not! There is something in JavaScript we can use to achieve the same features provided by Ruby Hashes: JavaScript Object Literals.

MDN defines an object literal as “a list of zero or more pairs of property names and associated values of an object.” As you can see from the definition, this is very similar to Ruby Hash‘s pairs of keys and associated values.

Here is a side-by-side comparison of creating, reading, changing, adding, and deleting a new JavaScript object literal versus a new Ruby hash literal:

JavaScript Object Literal:

//creating new JS object literal
var capitals = { spain: "Madrid",
  france: "Paris",
  italy: "Rome",
  hungary: "Budapest",
  germany: "Berlin"

//accessing JavaScript object value
capitals["france"]; //returns "Paris"
capitals["belgium"]; //returns undefined

//changing values
capitals["france"] = "Nice";

//adding a new property/value pair
capitals["russia"] = "Moscow";

//deleting a property/value pair
delete capitals["italy"];

//final result
{ spain: 'Madrid',
  france: 'Nice',
  hungary: 'Budapest',
  germany: 'Berlin',
  russia: 'Moscow' }
Ruby Hash Literal:

#creating new Ruby Hash literal
capitals = { spain: "Madrid",
  france: "Paris",
  italy: "Rome",
  hungary: "Budapest",
  germany: "Berlin"

#accessing Ruby hash value
capitals[:france] #returns "Paris"
capitals[:belgium] # returns nil

#changing values
capitals[:france] = "Nice"

#adding a new key/value pair
capitals[:russia] = "Moscow"

#deleting a key/value pair

#final result
p capitals
{:spain=>"Madrid", :france=>"Nice", :hungary=>"Budapest", :germany=>"Berlin", :russia=>"Moscow"}

See how similar they both are? Creating a JavaScript object literal is almost the same as creating a Ruby hash literal. It is important to note that while Ruby hash keys can be any data type (i.e. symbols, strings, integers, hashes, etc.), JavaScript object properties can only be variables. But they can point to any data type value, just like in Ruby hashes.

You can call a JavaScript object’s properties in a similar fashion as you would a Ruby hash‘s keys. Same with creating and deleting key/value and property/value pairs. Calling a non-existent key or property will return nil or undefined.

Note that while I used the bracket notation here to access and modify a JavaScript object’s properties, you can also use a dot notation. For a more in-depth explanation of the differences between the two types of notation, take a look at this medium article.

The next time you find yourself working with JavaScript and are looking to implement something similar to Ruby Hashes into your script, JavaScript object literals will fit the bill perfectly.

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