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.