As you may have noticed in Javascript there are only few primitive data types: Number, Strings, Boolean, null, and undefined. Anything else is considered an object. Objects are characterized by having property Key and Values.
As a QE, you'll be dealing with a lot of JSON objects specially when you are testing RESTFul API's. So it is imperative that you understand on how to work with objects.
Object properties often accessed by dot notation or bracket notation:
{% runkit %} let name = {"first_name": "Juan", "last_name": "Dela Cruz"}; typeof(name); console.log(name.first_name); // dot notation console.log(name["last_name"]); // bracket notation console["log"]("Hello, world!"); // console is an object too, you can use bracket notation when accessing its built-in methods. {% endrunkit %}
[IMPORTANT NOTE] it is often recommended to use dot notation instead. It is easier to type and read.
Object properties may also be nested. In order to access them, you just have to do a chained dot notation.
{% runkit %} let user = {"name": { "first_name": "Juan", "last_name": "Dela Cruz"}, "age": 26, "ids": [ "sss", "postal", "voter's"] };
console.log(user.name.first_name); console.log(user.ids); console.log(user.ids[0]); {% endrunkit %}
Objects can just be easily created in these ways:
{% runkit %} // Literal Method let user = {}; user.first_name = "Juan"; user.last_name = "Dela Cruz";
// or let another_user = {"first_name": "Juan", "last_name": "Dela Cruz"}; {% endrunkit %}
Objects may also contain methods as well:
{% runkit %} let user = {"name": { "first_name": "Juan", "last_name": "Dela Cruz"}, "age": 26, "ids": [ "sss", "postal", "voter's"], "printName": function() { console.log(this.name.first_name + " " + this.name.last_name) } };
user.printName(); {% endrunkit %}
Do take note the the this keyword refers to the object itself.
Objects can be changed during run time. You can assign new values to existing properties or even add/delete properties.
{% runkit %} let user = {"name": { "first_name": "Juan", "last_name": "Dela Cruz"}, "age": 26, "ids": [ "sss", "postal", "voter's"] };
// Add new property user.likes = ["adobo", "tinapa"];
// Change property user.name.first_name = "Juliana";
// Delete property delete user.ids; user; {% endrunkit %}
[IMPORTANT NOTE] Objects are never copied. If you assign an object to a new variable, the new variable will only store the reference on it. . This is coined as Pass by reference.
{% runkit %} let obj = {"first_name": "Juan", "last_name": "Dela Cruz"}; // Assign obj to a new variable let new_obj = obj;
// Now let's try to change the original obj obj.first_name = "William";
// You might assume that the another_obj still has the original "first_name" value of "Juan" console.log("obj: " + obj.first_name + " " + obj.last_name); console.log("new_obj: " + new_obj.first_name + " " + new_obj.last_name);
// This also applies to functions too function changeLastName(user, value) { user.last_name = value; }
changeLastName(new_obj, "Jennings");
// You might assume that the another_obj still has the original "first_name" value of "Juan" console.log("obj: " + obj.first_name + " " + obj.last_name); console.log("new_obj: " + new_obj.first_name + " " + new_obj.last_name);
{% endrunkit %}
All objects in javascript inherits properties from Object.prototype as documented here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/prototype. Built-in methods such as .toString() are inherited from this:
{% runkit %} let obj = {"first_name": "Juan", "last_name": "Dela Cruz"}; obj.toString(); obj; {% endrunkit %}
We will discuss this in more detail in the Classes section.