javascript - Input type number, decimal value

Question

How to verify if an input type number contain maximum 3 decimal, without using regex

let x = 1.5555
let y = 1.55
x is false
y is true

question from:https://stackoverflow.com/questions/65933337/input-type-number-decimal-value

Answer 1

You can use a formula like:

(x * 1000) % 1 === 0

For numbers with 3 or fewer decimal places, the x*1000 will convert it into an integer. Eg:

1.55 -> 1550
1.555 -> 1555 

For numbers with more than 3 decimal places, doing x*1000 won't convert it to an int, it will only shift parts of the number over:

1.5555 -> 1555.5 // still a decimal

The % 1 check then gets the remainder of the above number if it was to be divided by 1. If the remainder is 0, then the number was converted to an integer, if it is more than 0, then x*1000 failed to convert the number to an int, meaning that it has more than 3 decimals:

const validate = x => (x * 1000) % 1 === 0;

console.log(validate(1.5555)); // false
console.log(validate(1.55)); // true
console.log(validate(1.555)); // true
console.log(validate(0.00000001)); // false