JavaScript Numbers
A JavaScript number is any numeric value. Whole values and decimal values share this one type.
Whole and decimal
A JavaScript number is any numeric value, whole or decimal. The last value uses exponent form, a short way to write large values.
let count = 7;
let price = 19.99;
console.log(count);
console.log(price);
console.log(1e6);A decimal surprise
Adding decimals can leave a tiny error in the result.
console.log(0.1 + 0.2);Not a number
NaN is short for not a number, and it marks a failed calculation. Joining the value to a label with + turns it into text, so the console shows NaN itself.
console.log("Result: " + (0 / 0));
console.log(Number.isNaN(0 / 0));
console.log("Result: " + ("abc" * 2));Example
let price = 2.5;
let quantity = 4;
console.log(price * quantity);
console.log(0.1 + 0.2);
console.log("Check:", Number.isNaN(0 / 0));Key points
- Exponent form is a short way to write very large or very small values with the letter e.
- Decimal values are approximations, so a sum can carry a tiny error.
- NaN means not a number, and it is the result of an impossible calculation.
- Dividing a positive number by zero gives Infinity, a value beyond every finite number.
- Number.isNaN checks whether a value is NaN and reports true or false.
In this example, the program multiplies a decimal price by a whole quantity and prints 10. It then adds 0.1 and 0.2 and prints the approximate result. The last line checks 0 divided by 0 with Number.isNaN and prints true.
Try it Yourself
Edit the code, then press Run.
Runs in your browser — the preview under the editor is the real result. Nothing is sent to a server. The code runner panel (right) does the same with more room.
Exercise
What does 0.1 + 0.2 print?