Dynamic typing

JavaScript is a "dynamically typed language", which means that, unlike some other languages, you don't need to specify what data type a variable will contain (numbers, strings, arrays, etc).

For example, if you declare a variable and give it a value enclosed in quotes, the browser treats the variable as a string:

let myString = 'Hello';

Even if the value contains numbers, it is still a string, so be careful:

let myNumber = '500'; // oops, this is still a string
typeof myNumber;
myNumber = 500; // much better – now this is a number
typeof myNumber;

Try entering the four lines above into your console one by one, and see what the results are. You'll notice that we are using a special operator called typeof – this returns the data type of the variable you type after it. The first time it is called, it should return string, as at that point the myNumber variable contains a string, '500'. Have a look and see what it returns the second time you call it.