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Variables

There are two ways to declare a variable in javascript, using const and let.

let​

let word = "JavaScript";
console.log(word); // JavaScript

The above example shows how to declare a variable using let.

Note

Variable declared using let can be re-assigned later.

let word = "JavaScript";
word = "HTML"; // variable word is re-assigned with "HTML"
Note

let is used to create a variable whose value changes in the code.

const​

const word = "JavaScript";
console.log(word); // JavaScript
word = "HTML"; // ❌ Type error: this will break script
Note

Variables defined with const cannot be re-assigned.

let vs const​

How do you choose whether to use let or const? Const is always preferable until you realise you need to be able to re-assign the variable later on, at which point you should switch to let.

For example, if you define a variable count (which you expect to increment), you will immediately recognise it and use let.

The advantage of using const is that once a variable is declared as an array, it will remain an array indefinitely (but as you will see later on, the elements inside the array might change). Because you know the variable will always be of type array, you can confidently use array methods on it.

Note

Even though var still works, its use is discouraged because it can be confusing in a variety of situations. As a result, you can simply replace var with let (or const if the variable is not being reassigned).

When defining variables, avoid the use of var. Use let or const instead.