Text and Numbers

Every value in JavaScript has a type. So far, you've used two types:

• numbers, such as 25 or 1.5, which you can calculate with;
• text, such as "Hello". Programmers call it a string, as in a string of characters.

That's why text needs quotes and numbers don't: 25 is a number, but "25" is text made of the characters 2 and 5. The type decides what an operator does. For example, + adds two numbers, but joins two strings:

console.log(5 + 3);
console.log("5" + "3");
console.log("5" + 3);

This prints:

8
53
53

The last line surprises many people. When one side of + is a string, JavaScript turns the other side into a string too, and joins them. That's why you can join text with numbers: "I am " + 25 + " years old." gives "I am 25 years old."

In the output, you can't see the type: console.log(5) and console.log("5") both print 5. To find out the type of a value, use typeof:

console.log(typeof 5);
console.log(typeof "5");

This prints:

number
string

typeof works with variables too: typeof price gives the type of the value stored in price.

A typical mistake is a number in quotes. Then + joins instead of adding, and the result looks strange:

const apples = "5";
console.log(apples + 1);

This prints 51 instead of 6. When a result surprises you like this, check the types with typeof.