In programming, a variable is a holder (storage area) to hold information. For example,
let num = 5;
Here, num is the variabe that holds the number 5.
var x; let y;
Here, x and y are variables.
Both var and let are used to declare variables. Be that as it may, there are a few differences between them.
|var is function scoped (will be discussed in later tutorials).||let is block scoped (will be discussed in later tutorials).|
|For example, var x;||For example, let y;|
We use the assignment operator = to allocate an incentive to a variable.
let x; x = 5;
Here, 5 is assigned to variable x.
You can likewise initialize variables during its announcement.
let x = 5; let y = 6;
let x = 5, y = 6, z = 7;
If you use a variable without instating it, it will have an undefined value.
let x; // x is the name of the variable console.log(x); // undefined
Here x is the variable name and since it doesn’t contain any worth, it will be undefined.
You will learn about undefined and other data types in the next tutorial in detail.
Change the Value of Variables
It’s conceivable to change the value stored in the variable. For instance,
// 5 is assigned to variable x let x = 5; console.log(x); // 5 // vaue of variable x is changed x = 3; console.log(x); // 3
The value of a variable may vary. Hence, the name variable.
The rules for naming variables are:
- Variable names should begin with either a letter, an underscore _, or the dollar sign $. For instance,
//valid let a = 'hello'; let _a = 'hello'; let $a = 'hello';
2. Variable names cannot start with numbers. For example,
//invalid Let 1a = 'hello'; // this gives an error
let y = "hi"; let Y = 5; console.log(y); // hi console.log(Y); // 5
4. Keywords cannot be used as variable names. For example,
//invalid let new = 5; // Error! new is a keyword.
Despite the fact that you can name variables in any capacity you need, it’s a decent practice to give an enlightening variable name. If you are using a variable to store the number of apples, it better to use apples or numberOfApples as opposed to x or n.
The const keyword was also introduced in the ES6(ES2015) version to create constants. For example,
const x = 5;
Once a constant is initialized, we cannot change its value.
const x = 5; x = 10; // Error! constant cannot be changed. console.log(x)
Simply, a constant is a type of variable whose value cannot be changed.
Also, you cannot declare a constant without initializing it. For example,
const x; // Error! Missing initializer in const declaration. x = 5; console.log(x)
Now that you know about variables, you will learn about different types of data a variable can store in the next tutorial.
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