JavaScript: Convert a number in bytes to a human-readable string

JavaScript fundamental (ES6 Syntax): Exercise-163 with Solution

Bytes to Human-Readable String

Write a JavaScript program to convert a number in bytes to a human-readable string.

Note: Use an array dictionary of units to be accessed based on the exponent.

• Use an array dictionary of units to be accessed based on the exponent.
• Use Number.prototype.toPrecision() to truncate the number to a certain number of digits.
• Return the prettified string by building it up, taking into account the supplied options and whether it is negative or not.
• Omit the second argument, precision, to use a default precision of 3 digits.
• Omit the third argument, addSpace, to add space between the number and unit by default.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
// Define a function 'prettyBytes' to convert a number of bytes into a human-readable string representation
const prettyBytes = (num, precision = 3, addSpace = true) => {
  // Define an array of units in increasing order of size
  const UNITS = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
  // If the absolute value of the number is less than 1, return it with the smallest unit 'B'
  if (Math.abs(num) < 1) return num + (addSpace ? ' ' : '') + UNITS[0];
  // Determine the appropriate unit based on the magnitude of the number
  const exponent = Math.min(Math.floor(Math.log10(num < 0 ? -num : num) / 3), UNITS.length - 1);
  // Calculate the value in the chosen unit with the specified precision
  const n = Number(((num < 0 ? -num : num) / 1000 ** exponent).toPrecision(precision));
  // Construct and return the human-readable string representation
  return (num < 0 ? '-' : '') + n + (addSpace ? ' ' : '') + UNITS[exponent];
};

// Test cases
console.log(prettyBytes(1000)); // Output: 1 KB
console.log(prettyBytes(-27145424323.5821, 5)); // Output: -27.145 TB
console.log(prettyBytes(123456789, 3, false)); // Output: 123MB

Sample Output:

1 KB
-27.145 GB
123MB

Pictorial Presentation:

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-163-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that converts a byte count into a human-readable string using appropriate units (KB, MB, GB).
• Write a JavaScript function that formats a file size in bytes into a string with one decimal place and unit suffix.
• Write a JavaScript program that takes a number in bytes and outputs a localized human-readable format.
• Write a JavaScript program that converts large byte values to a readable string using logarithms to determine the unit.

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