How to round to at most 2 decimal places, if necessary

Handling diverse rounding scenarios

From quick fixes to advanced methods, here's a range of solutions when dealing with different rounding scenarios:

String manipulation approach

Using strings to round numbers minimizes floating-point irregularities in JavaScript. Here, we'll utilize the exponential notation for higher precision:

// String operation solution for the mathematician allergic to numbers
const roundViaString = (num, decimals) => {
  const factor = Math.pow(10, decimals);
  return parseFloat((Math.round((+num + Number.EPSILON) * factor) / factor).toExponential(decimals));
};


Battle tricky values

In JavaScript, certain values like 1.005 may pose a challenge due to binary floating-point representation. Here's a solution:

• Double rounding: Implementing Number.toPrecision prior to Math.round drastically minimizes errors.
• Pre-rounding: Consider rounding numbers server-side before they reach JavaScript for more robust accuracy.
• Phase in the pros: Invoke professional libraries like decimal.js for increased precision in crucial applications.

Implementing dynamic precision

Customize precision based on your needs with a custom function:

// A dynamic precision solution for the precision savvy.
const roundNumber = (num, scale) => {
  if (!("" + num).includes("e")) {
    return +(Math.round(num + "e+" + scale) + "e-" + scale);
  } else {
    const arr = ("" + num).split("e");
    let sig = "";
    if (+arr[1] + scale > 0) {
      sig = "+";
    }
    return +(Math.round(+arr[0] + "e" + sig + (+arr[1] + scale)) + "e-" + scale);
  }
};


Small numbers need love too

Tiny numbers require extra care for accurate rounding in JavaScript:

// A small solution for small problems.
const roundTinyNumber = (num, decimals) => {
  return Math.round((num + Number.EPSILON) * Math.pow(10, decimals)) / Math.pow(10, decimals);
};


Building a rounding code toolbox

Enhance your rounding skills with these additional techniques:

• Exponential control: Converting numbers to exponential form attains more control over the rounding process.
• Rounding tests: Crafting assertive tests in your code checks the integrity of the rounding outcomes.
• Tailored rounding: Accommodating specific rounding requirements using custom methods optimizes the rounding precision.