JavaScript Invocation Context(this) Interview Questions

JavaScript can deal with different kinds of values.

Number value

Here is an example of number values.

23;
67.21;

Some programming language consider above two numbers as different types, like int and float. But, JavaScript consider both as a number value. There is no distinction between a number with decimal and without decimal in JavaScript.

String value

When a value is wrapped with double quotes("") or single quotes('') or back tick(``), that is a string value in JavaScript.

"I am a string";
"I am a string"`I am a string`;

Boolean value

Two values in JavaScript are boolean values. They are true and false.

null and undefined

The values null and undefined are referred to as empty values in JavaScript.

undefined value denotes a declared variable but not assigned. So in JavaScript, we declare a variable and try to get its value, undefined is returned.

var a;
console.log(a); // undefined.

null value is used to mark an intentional absense of an object. Say, we have a function that returns an object. If that function does not have an object to return, it should return null.

Example. match() is a string method that returns an array of all matches in a string based on a regular expression.

var str = "Backbencher is the new frontbencher";
var result = str.match(/apple/g);
console.log(result); // null

In the above code, we are searching for string "apple" in str. If there is a match, the method returns an Array. Since there is no match, it returned null.

In JavaScript, a function that returns an object should never return undefined to tell intentional absense of an object. It is because, a function by default returns undefined during invocation. So we cannot distinguish the origin of undefined and what purpose it serves.

Array values

Array is a collection of values. The values can be of any type. We represent an array using [] syntax.

Here are some examples.

[1, 2, 3][("Apple", "Banana", "Orange")][(2, "John", 4.89)];

Array is an example of data structure that stores each element in contiguous memory locations.

Object values

Objects are another kind of data structure in JavaScript that store data in key value pairs.

Example:

{
  name: "John Doe",
  age: 23
}

Values and its different types in JavaScript help us to perform various kinds of operations on them.