JavaScript - format size in bytes to human-readable (KB, MB, GB, TB, PB)

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const SHORT_UNITS = ['B', 'KB', 'MB', 'GB', 'TB', 'PB'];
const FULL_UNITS = ['bytes', 'kilobytes', 'megabytes', 'gigabytes', 'terabytes', 'petabytes'];

// Source: https://dirask.com/snippets/JavaScript-round-floating-point-number-with-precision-Dd53lp
//
const roundNumber = (value, precision = 0) => {
    if (precision > 0) {
        const power = Math.pow(10, precision);
        return Math.round(value * power) / power; 
    }
    return Math.round(value);
};

const calculateSize = (bytes, units = SHORT_UNITS) => {
    if (bytes === 0) {
        return {
            value: 0,
            unit: units[0] ?? 'B'
        }; 
    }
    const level = Math.floor(Math.log(bytes) / Math.log(1024));
    const index = Math.min(level, units.length - 1);
    return {
        value: bytes / Math.pow(1024, index),
        unit: units[index] ?? 'B'
    };
};

const renderSize = (bytes, precision = 2, units = SHORT_UNITS, spacer = '') => {
    const size = calculateSize(bytes, units);
    const value = roundNumber(size.value, precision);
    return value + spacer + size.unit;
};

const printSize = (bytes, precision = 2, units = SHORT_UNITS, spacer = '') => {
    console.log(renderSize(bytes, precision, units, spacer));
};



// ---------------------------------------------------------
// Practical example 1 (used pre-default SHORT_UNITS units):
// ---------------------------------------------------------

console.log(renderSize(512));               // 512B
console.log(renderSize(1536));              // 1.5KB
console.log(renderSize(1572864));           // 1.5MB
console.log(renderSize(1610612736));        // 1.5GB
console.log(renderSize(1649267441664));     // 1.5TB
console.log(renderSize(1688849860263936));  // 1.5PB



// ---------------------------------------------------------
// Practical example 2 (used pre-default SHORT_UNITS units):
// ---------------------------------------------------------

console.log(renderSize(1024));                              // 1KB
console.log(renderSize(1024 * 1024));                       // 1MB
console.log(renderSize(1024 * 1024 * 1024));                // 1GB
console.log(renderSize(1024 * 1024 * 1024 * 1024));         // 1TB
console.log(renderSize(1024 * 1024 * 1024 * 1024 * 1024));  // 1PB



// ---------------------------------------------------------
// Practical example 3 (used pre-default SHORT_UNITS units):
// ---------------------------------------------------------

//                          precision (decimal numbers)
//                              |
//                              v
console.log(renderSize(1234567, 0));  // 1MB
console.log(renderSize(1234567, 1));  // 1.2MB
console.log(renderSize(1234567, 2));  // 1.18MB
console.log(renderSize(1234567, 3));  // 1.177MB
console.log(renderSize(1234567, 4));  // 1.1774MB
console.log(renderSize(1234567, 5));  // 1.17737MB
console.log(renderSize(1234567, 6));  // 1.177375MB



// ---------------------------------------------------------
// Practical example 4 (used FULL_UNITS units):
// ---------------------------------------------------------

console.log(renderSize(1234567, 0, FULL_UNITS, ' '));  // 1MB
console.log(renderSize(1234567, 1, FULL_UNITS, ' '));  // 1.2MB
console.log(renderSize(1234567, 2, FULL_UNITS, ' '));  // 1.18MB
console.log(renderSize(1234567, 3, FULL_UNITS, ' '));  // 1.177MB
console.log(renderSize(1234567, 4, FULL_UNITS, ' '));  // 1.1774MB
console.log(renderSize(1234567, 5, FULL_UNITS, ' '));  // 1.17737MB
console.log(renderSize(1234567, 6, FULL_UNITS, ' '));  // 1.177375MB



// ---------------------------------------------------
// See also:
// ---------------------------------------------------
//
//     1. https://dirask.com/snippets/JavaScript-parse-file-size-to-bytes-input-in-B-KB-MB-GB-TB-PB-Ddkq31