Javascript human readable byte size function

31 March, 2020

Here is a small function which converts a bytes in to a readable format (B, KB, MB, GB, TB).

Function

const TB = 1000000000000;
const GB = 1000000000;
const MB = 1000000;
const KB = 1000;

function bytesReadable(byteSize, decimals) {
    let unit;
    let i;
    let remainder;

    // Get the whole number, and the remainder for the
    // decimals later on.
    if (byteSize > TB) {
        unit = "TB";
        i = Math.floor(byteSize / TB);
        remainder = byteSize - (i * TB);
    }else if (byteSize > GB) {
        unit = "GB";
        i = Math.floor(byteSize / GB);
        remainder = byteSize - (i * GB);
    }else if (byteSize > MB) {
        unit = "MB";
        i = Math.floor(byteSize / MB);
        remainder = byteSize - (i * MB);

    }else if (byteSize > KB){
        unit = "KB";
        i = Math.floor(byteSize / KB),
            remainder = byteSize - i * KB;
    }else{
        // Can't go smaller than bytes!
        return i.toString() + " " + unit;
    }

    if (decimals === 0){
        return i.toString() + " " + unit;
    }

    // Now we calculate the eventual missing leading
    // zeroes to pad up if needed.
    let width;
    if (remainder > GB){
        width = 12;
    }else if (remainder > MB){
        width = 9;
    }else if (remainder > KB){
        width = 6;
    }else{
        width = 3;
    }

    // Fill up leading zeroes if they are missing
    let remainderString = remainder.toString();

    for (let i = remainderString.length; i < width; i++){
        remainderString = "0" + remainderString;
    }

    // Check to prevent unwanted behaviour
    if (decimals > remainderString.length){
        decimals = remainderString.length;
    }

    return i.toString() + "." + remainderString.substr(0, decimals) + " " + unit;
}

Sample

console.log(bytesReadable(425005, 2));
console.log(bytesReadable(8741208, 2));
console.log(bytesReadable(114448910, 2));
console.log(bytesReadable(557891, 2));
console.log(bytesReadable(114710, 2));
console.log(bytesReadable(8933578, 2));
console.log(bytesReadable(5849684981, 2));
console.log(bytesReadable(12033687, 2));
console.log(bytesReadable(742289, 2));
console.log(bytesReadable(678007439, 2));

// Output
425.00 KB
  8.74 MB
114.44 MB
557.89 KB
114.71 KB
  8.93 MB
  5.84 GB
 12.03 MB
742.28 KB
678.00 MB