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Demystifying JavaScript: let, var, and const Explained with Examples

Jack Pritom Soren on February 16, 2024

JavaScript, being a versatile and widely-used programming language, offers several ways to declare variables, namely let, var, and const. Understan...
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Eckehard •

While everything you explained was quite correct, it can be helpful to mention, that things might be quite different in some situations.

let a = {}

a.a=10
a.b=20
a.c=a.a*a.b

console.log(a) //-> { a: 10, b: 20, c: 200 }
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"a" is an Object, properties can be used as variables, but they do not need to be declared in Javascript.

Things get even stranger if you use Classes:

class c {
  constructor(){
    this.a = 10
    this.b = 20
  }
  mul(){ return this.a * this.b }
}
let OB = new c()
console.log(OB.mul())
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Variables inside a class need to be prefixed by "this", but they do not need let or const either. Also, methods (= functions of a class ) do not need to be defined at all, you just write down the name()

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kvetoslavnovak •

What is the point to mix varaiables with properties and methods of an object?

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Eckehard •

The point is the different syntax and the different rules. You cannot - for example - define a constant inside a class. It lies in the history of JS, but is not helpful in any way.

In most other languages you can use the same code in a function or in a class method (= function). In JS you have to rewrite anything, even if you want to do the exact same thing. That is at least confusing.

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Maxim Klochkov • • Edited

I think you have a mistake in your var Example - message is defined within a function scope so priniting it out in global scope will produce an error:

console.log(message); // message is not defined
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