5. Types

sum with a value of 99 is a variable of type (number). In addition to numbers, JS also uses other data types:

string - a string of characters. They are written in quotation marks or apostrophes, e.g. ‘JS programmers are cool’

variable of logical type (boolean)- true (logical truth) lub false (logical false)

null- meaning an empty object

undefined- undefined value

To check the type of a variable, you can use typeof, for example, typeof sum.

Now, try creating a variable with your name. In the console, type let name = "enter your name here";. Then, write console.log(name);. You should see your name in the console. Check the type of your name variable by typing console.log(typeof name); in the console.

Spróbuj teraz stworzyć zmienną ze swoim imieniem. W konsoli wpisz let name = "tu podaj swoje imię"; Następnie napisz console.log(name);. Powinnaś zobaczyć swoje imię w konsoli. Sprawdź jakiego typu jest Twoja zmienna name przez wpisanie w konsoli console.log(typeof name);

Numbers and Operators

We can perform mathematical operations on numbers using operators, as shown in the table below.

Let’s assume we have following variables:

let y = 8;

let z = 4;

Now, try writing a few of these operations in the console. First, create two arbitrary number variables, and then use console.log to print the results of the operations in the console.

Strings

We can also perform certain operations on strings, for example we can add them to each other (this is called concatenation).

let text_1 = "Hello";
let text_2 = "Jack";
let text_3 = text_1 + ', ' + text_2 + '!'; // Hello, Jack!

Create a variable named surname and assign it your last name. Then, define another variable named fullName and make its value your two previous variables, so your name and surname, separated by a space. Print the value of the fullName variable in the console.

The length property is used to determine the length of a string.

text_3.length; // 12

Check the lengths of three of your string variables (name, surname, fullName) by printing them in the console.

We can also change the case of characters in a string to uppercase or lowercase:

text_3.toUpperCase(); // HELLO, JACK!
text_3.toLowerCase(); // hello, jack!

Make your name in the name variable uppercase.

Another method is to check the position of a substring within a string:

text_3.indexOf('Jack'); // 7

Find out the position of the letter ‘a’ in your first name.

We can also replace parts of a string:

text_3.replace('Jack', 'Mary');

This will replace the first occurrence of the given string (in our case ‘Jack’) with a new string (‘Mary’).

Task

Create a variable named hello and assign the following text to it: “Hello, [enter your name]!”. Then, using the replace method, modify the text to look like this: “Hello, JavaScript!”.