Developer Notes

JavaScript: Number rounding

July 21, 2021

So to be able to round a number in JavaScript I found that this is the best and easy way. This way I don’t have to convert the Number to String to cut some digits and the transform it back to Number

1/**
2 *  @param value - number - Number to round
3 *  @param decimals - number - how many digits after the `.`
4 *  @return number
5 */
6function round(value, decimals) {
7  return Number(Math.round(`${value}e${decimals}`) + 'e-' + decimals);
8}

To prove it, here is a test for it

1describe('Number rounding', () => {
2  it('should return expected value', () => {
3    [
4      [2.1234, 2.12, 2],
5      [2.125, 2.13, 2],
6      [2.11111, 2.11, 2],
7      [2.11115, 2.1112, 4],
8      [2.123, 2, 0],
9      [2.123, NaN, 0],
10      ["2.123", 2.12, 2]
11    ].forEach(([value, expectedValue, decimals]) => {
12      expect(round(value, decimals)).toBe(expectedValue)
13    })
14  })
15})

My name is Bozhidar Dryanovski and I'm a Software Engineer at Clarity
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