Integers and decimals

Learn integer and decimal numbers and that JavaScript has a single number type.

One type: number

In JavaScript all numbers live under a single type: number. There is no separate integer and float type; both belong to the same type.

For example 7 is an integer and 3.14 is a decimal number. The part left of the dot is the whole part, the part right of it is the decimal part. Negative numbers belong to the same type: -5 or -0.5.

When you add two numbers the result is still a number. The typeof operator returns "number" for both.

Careful with decimals

Decimal numbers are stored in binary on computers. Because of this some values cannot be shown exactly and small rounding errors appear.

For example 0.1 + 0.2 does not give 0.3; it gives 0.30000000000000004. This is not specific to JavaScript; all languages behave this way.

When working with money most people keep the amount as an integer in cents or use rounding functions to avoid these errors.

Exercise Declare quantity and price

Declare an integer const variable named quantity with value 3. Declare a decimal const variable named price with value 19.99. Then log both with console.log.

Show example solution

const quantity = 3;
const price = 19.99;
console.log(quantity);
console.log(price);

Test yourself

Which one is a decimal (float) number?
- 42
- 3.14
- -8
- 1000
Show answer

3.14 — Correct. 3.14 is a decimal number; values with a dot count as floats.
Decimal price
```
const price = ____;
```
Show answer
```
const price = 19.99;
```
Match each term to its meaning

integer

Whole number (7, -3)
float

Decimal number (3.14)
number

JS's single number type
typeof

Returns the type of a value
What does console.log(typeof 42); print?
```
console.log(typeof 42);
```
- "number"
- "integer"
- "42"
- "int"
Show answer

"number" — Correct. JavaScript keeps integers and decimals in the same type; typeof returns "number" for both.

Next lesson: The Math object

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