How to add test unit in js

Question

let number = 64.129922
console.log(number - 10); //here i need only minus last 2 

console.log(number - 10); //here i need only   

le.log(number - 10); //here i need only minus last 2

Answer 1

You cannot reliably use the number of digits after the decimal in a number. The number type doesn't have any concept of how many digits are after the decimal (and the algorithm to determine how many to include when creating a string for the number is complex.

If you always want to adjust the values you're subtracting to turn 10 into .00001 and 1 into .000001 , etc., then what you're doing is dividing them by 1,000,000:

 function addAdjusted(base, addend) { return base + (addend / 1000000); } console.log(addAdjusted(64.131577, -10)); // 64.131567 (roughly) console.log(addAdjusted(64.131577, -1)); // 64.131576 (roughly) console.log(addAdjusted(64.131577, -76)); // 64.131501 (roughly)

Note that at those scales, the number type becomes fairly imprecise . If you're going to output the results as strings, you might consider using toFixed(6) to adjust the output:

 function addAdjusted(base, addend) { return base + (addend / 1000000); } console.log(addAdjusted(64.131577, -10).toFixed(6)); // "64.131567" console.log(addAdjusted(64.131577, -1).toFixed(6)); // "64.131576" console.log(addAdjusted(64.131577, -76).toFixed(6)); // "64.131501"