JavaScript Recipe: Round to a number of decimal places stripping trailing zeros

JS uses binary floating point to handle decimal based operations.

JavaScript calculations with floating point causes the Nonsense cases especially during the result comparisons & displaying.

If the variable was created as a Number, not a String, extra trailing zeros would be dropped automatically.

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Round to a maximum number of fraction digits

• toFixed() - round to the last indicated decimal position.

    var n = 50.777;
    n.toFixed(2);          // "50.78"
  

  Watchout: it returns a String!

  Note: it will return extra trailing digits if the number of places is higher, than actual number of fraction digits:

    95.56789.toFixed(5);   // "50.77700"
  

Remove insignificant trailing zeros from number

If you define number with trailing zeros they're dropped:

var n = 50.77700;
// n = 50.777

• parseFloat() - converts a strings with decimals into numbers; so it will automatically drop any trailing 0's

    var n = "50.77700";
    parseFloat(n);        // 50.777
  

Round to a number of places and drop trailing zeros

JavaScript

function roundDecimal(value, maxFractionDigits) {
  if (!isItDamnNumber(value) || !isItDamnNumber(maxFractionDigits)) {
    throw "Number is expected as an argument!"
  }
  return parseFloat(value.toFixed(maxFractionDigits))
}

function isItDamnNumber(data) {
    return typeof data === "number" && !isNaN(data);
}

Here how it looks in TypeScript:

TypeScript

const roundDecimal = (val: number, maxFractionDigits: number): string => {
  return parseFloat(val.toFixed(maxFractionDigits)).toString();
};

console.log(roundDecimal(50.77, 10));  // '50.77'

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see Also

• Best Practice: Watchout Wacky Decimals in JavaScript
• Best Practice: Comparisons in JavaScript;
• Best Practice: Executions & Memory Control in JavaScript
• Best Practice: Loops Optimization
• Fun with an Algorithm complexity
• JS - The Right Way
• Tutorials Point - Best Practices
• Keynote: Top JS frmeworks 2015