Learn Storing Data | Manipulating Data

Definition

Variables are containers of data in a computer's memory. The general syntax of creating a new variable is let variableName.

For example, the following code declares a new variable called username:

let username;

This is known as a Variable Declaration Statement.

We can assign a value to a variable using the syntax variableName = data, where data can be some text, number, or any other valid data type.

For example:

let username;
username = "John Smith";

The statement in which we assign some value to a variable is known as an Assignment Statement.

We can simply use the variable name for accessing data from it:


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let username;
username = "John Smith";
console.log(username);

In the above code, the term username was passed as an argument to the console.log statement. This simply fetches whatever is inside the username and passes it into the console.log, which in turn displays the data on the screen.

If a variable is not assigned any value, it holds the value undefined by default:


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let exampleVar;
console.log(exampleVar);

Assigning a value to a variable for the first time is known as Initialization.

There is a shorter syntax for declaring and initializing a variable at the same time: let variableName = data;:


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let username = "John Doe";
console.log(username);

Two variables cannot have the same names, otherwise it would result in an error:


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let variableA;
let variableA; // Error at this line

However, it's also important to note that the variable names are case-sensitive, so variableA and VariableA are considered as two different names.

Furthermore, there are some naming rules for the variable which we need to follow:

The variable names cannot begin with a number;
Variable names cannot contain special characters except $ and _;
Variable names cannot be the same as any reserved keyword that JavaScript uses. For example, using let or const as a variable name is not allowed.

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Section 2. Chapter 1

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