Every programming language have a way to make variables. Remember the part where I explained literals and identifiers? Well a variable is an identifier with literal value assigned to it. It's like a virtual box that can hold values you put into it. We'll learn them by examples in this section.
let keyword indicates that the statement will create a binding between variable name and value:
let name = "Nathan"; // bind variable name "name" to string value "Nathan" console.log(name); // Nathan name = "Sebhastian"; // can you guess this one? console.log(name); // Sebhastian
As you can see, the name variable I created was first assigned the value "Nathan", and then changed to "Sebhastian". You can also declare multiple variables using the same
let firstName = "Nathan", // don't forget this comma lastName = "Sebhastian"; console.log (firstName); console.log (lastName);
If you don't specify any value during variable declaration, the value of the variable will be undefined until your code store a new value into it.
let age; console.log (age); // undefined age = 25; console.log (age); // 25
That's pretty much explain
var if they could, since var can introduce bugs that can be avoided using
var firstName = "Nathan", // you will hardly notice any difference in the result. lastName = "Sebhastian"; console.log (firstName); console.log (lastName);
The bottom line you need to remember is this:
let is new and recommended way to declare variable since ES2015.
Variables declared using
const keyword CANNOT be changed after its declaration. This variable is used for special situations where the value of the variable need to remain the same throughout runtime.
const name = "Nathan"; name = "Jeremy"; // will throw TypeError: Assignment to constant variable.
That will be everything you need to know about variables for now. Let's move on to data types.