Converting file size in bytes to human-readable st

问题:

I'm using this function to convert a file size in bytes to a human-readable file size:

function getReadableFileSizeString(fileSizeInBytes) {
    var i = -1;
    var byteUnits = [' kB', ' MB', ' GB', ' TB', 'PB', 'EB', 'ZB', 'YB'];
    do {
        fileSizeInBytes = fileSizeInBytes / 1024;
        i++;
    } while (fileSizeInBytes > 1024);

    return Math.max(fileSizeInBytes, 0.1).toFixed(1) + byteUnits[i];
};

However, it seems like this isn't 100% accurate. For example:

getReadableFileSizeString(1551859712); // output is "1.4 GB"

Shouldn't this be "1.5 GB"? It seems like the division by 1024 is losing precision. Am I totally misunderstanding something or is there a better way to do this?

回答1:

It depends on whether you want to use the binary or decimal convention.

RAM, for instance, is always measured in binary, so to express 1551859712 as ~1.4GiB would be correct.

On the other hand, hard disk manufacturers like to use decimal, so they would call it ~1.6GB.

And just to be confusing, floppy disks use a mixture of the two systems - their 1MB is actually 1024000 bytes.

回答2:

Here's one I wrote:

function humanFileSize(bytes, si) {
    var thresh = si ? 1000 : 1024;
    if(Math.abs(bytes) < thresh) {
        return bytes + ' B';
    }
    var units = si
        ? ['kB','MB','GB','TB','PB','EB','ZB','YB']
        : ['KiB','MiB','GiB','TiB','PiB','EiB','ZiB','YiB'];
    var u = -1;
    do {
        bytes /= thresh;
        ++u;
    } while(Math.abs(bytes) >= thresh && u < units.length - 1);
    return bytes.toFixed(1)+' '+units[u];
}

e.g.

humanFileSize(5000,true)
> "5.0 kB"
humanFileSize(5000,false)
> "4.9 KiB"
humanFileSize(-10000000000000000000000000000)
> "-8271.8 YiB"

回答3:

Another embodiment of the calculation

function humanFileSize(size) {
    var i = Math.floor( Math.log(size) / Math.log(1024) );
    return ( size / Math.pow(1024, i) ).toFixed(2) * 1 + ' ' + ['B', 'kB', 'MB', 'GB', 'TB'][i];
};

回答4:

Here is a prototype to convert a number to a readable string respecting the new international standards.

There are two ways to represent big numbers: You could either display them in multiples of 1000 = 10 3 (base 10) or 1024 = 2 10 (base 2). If you divide by 1000, you probably use the SI prefix names, if you divide by 1024, you probably use the IEC prefix names. The problem starts with dividing by 1024. Many applications use the SI prefix names for it and some use the IEC prefix names. The current situation is a mess. If you see SI prefix names you do not know whether the number is divided by 1000 or 1024

https://wiki.ubuntu.com/UnitsPolicy

http://en.wikipedia.org/wiki/Template:Quantities_of_bytes

Object.defineProperty(Number.prototype,'fileSize',{value:function(a,b,c,d){
 return (a=a?[1e3,'k','B']:[1024,'K','iB'],b=Math,c=b.log,
 d=c(this)/c(a[0])|0,this/b.pow(a[0],d)).toFixed(2)
 +' '+(d?(a[1]+'MGTPEZY')[--d]+a[2]:'Bytes');
},writable:false,enumerable:false});

This function contains no loop, and so it's probably faster than some other functions.

Usage:

IEC prefix

console.log((186457865).fileSize()); // default IEC (power 1024)
//177.82 MiB
//KiB,MiB,GiB,TiB,PiB,EiB,ZiB,YiB

SI prefix

console.log((186457865).fileSize(1)); //1,true for SI (power 1000)
//186.46 MB 
//kB,MB,GB,TB,PB,EB,ZB,YB

i set the IEC as default because i always used binary mode to calculate the size of a file... using the power of 1024

---

If you just want one of them in a short oneliner function:

SI

function fileSizeSI(a,b,c,d,e){
 return (b=Math,c=b.log,d=1e3,e=c(a)/c(d)|0,a/b.pow(d,e)).toFixed(2)
 +' '+(e?'kMGTPEZY'[--e]+'B':'Bytes')
}
//kB,MB,GB,TB,PB,EB,ZB,YB

IEC

function fileSizeIEC(a,b,c,d,e){
 return (b=Math,c=b.log,d=1024,e=c(a)/c(d)|0,a/b.pow(d,e)).toFixed(2)
 +' '+(e?'KMGTPEZY'[--e]+'iB':'Bytes')
}
//KiB,MiB,GiB,TiB,PiB,EiB,ZiB,YiB

Usage:

console.log(fileSizeIEC(7412834521));

if you have some questions about the functions just ask

回答5:

sizeOf = function (bytes) {
  if (bytes == 0) { return "0.00 B"; }
  var e = Math.floor(Math.log(bytes) / Math.log(1024));
  return (bytes/Math.pow(1024, e)).toFixed(2)+' '+' KMGTP'.charAt(e)+'B';
}

sizeOf(2054110009);
//=> "1.91 GB"

sizeOf(7054110);
//=> "6.73 MB"

sizeOf( (3*1024*1024) );
//=> "3.00 MB"

回答6:

Solution as ReactJS Component

Bytes = React.createClass({
    formatBytes() {
        var i = Math.floor(Math.log(this.props.bytes) / Math.log(1024));
        return !this.props.bytes && '0 Bytes' || (this.props.bytes / Math.pow(1024, i)).toFixed(2) + " " + ['Bytes', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'][i]
    },
    render () {
        return (
            <span>{ this.formatBytes() }</span>
        );
    }
});

UPDATE For those using es6 here is a stateless version of this same component

const sufixes = ['Bytes', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
const getBytes = (bytes) => {
  const i = Math.floor(Math.log(bytes) / Math.log(1024));
  return !bytes && '0 Bytes' || (bytes / Math.pow(1024, i)).toFixed(2) + " " + sufixes[i];
};

const Bytes = ({ bytes }) => (<span>{ getBytes(bytes) }</span>);

Bytes.propTypes = {
  bytes: React.PropTypes.number,
};

回答7:

Based on cocco's idea, here's a less compact -but hopefully more comprehensive- example.

<!DOCTYPE html>
<html>
<head>
<title>File info</title>

<script>
<!--
function fileSize(bytes) {
    var exp = Math.log(bytes) / Math.log(1024) | 0;
    var result = (bytes / Math.pow(1024, exp)).toFixed(2);

    return result + ' ' + (exp == 0 ? 'bytes': 'KMGTPEZY'[exp - 1] + 'B');
}

function info(input) {
    input.nextElementSibling.textContent = fileSize(input.files[0].size);
} 
-->
</script>
</head>

<body>
<label for="upload-file"> File: </label>
<input id="upload-file" type="file" onchange="info(this)">
<div></div>
</body>
</html> 

回答8:

Another example similar to those here

function fileSize(b) {
    var u = 0, s=1024;
    while (b >= s || -b >= s) {
        b /= s;
        u++;
    }
    return (u ? b.toFixed(1) + ' ' : b) + ' KMGTPEZY'[u] + 'B';
}

It measures negligibly better performance than the others with similar features.

回答9:

Here's mine - works for really big files too -_-

function formatFileSize(size)
{
    var sizes = [' Bytes', ' KB', ' MB', ' GB', ' TB', ' PB', ' EB', ' ZB', ' YB'];
    for (var i = 1; i < sizes.length; i++)
    {
        if (size < Math.pow(1024, i)) return (Math.round((size/Math.pow(1024, i-1))*100)/100) + sizes[i-1];
    }
    return size;
}

回答10:

Based on cocco's answer but slightly desugerified (honestly, ones I was comfortable with are remained/added) and doesn't show trailing zeros but still supports 0, hope to be useful for others:

function fileSizeSI(size) {
    var e = (Math.log(size) / Math.log(1e3)) | 0;
    return +(size / Math.pow(1e3, e)).toFixed(2) + ' ' + ('kMGTPEZY'[e - 1] || '') + 'B';
}


// test:
document.write([0, 23, 4322, 324232132, 22e9, 64.22e12, 76.22e15, 64.66e18, 77.11e21, 22e24].map(fileSizeSI).join('<br>'));

回答11:

I wanted the "file manager" behavior (e.g., Windows Explorer) where the number of decimal places is proportional to the number size. Seemingly none of the other answers does this.

function humanFileSize(size) {
    if (size < 1024) return size + ' B'
    let i = Math.floor(Math.log(size) / Math.log(1024))
    let num = (size / Math.pow(1024, i))
    let round = Math.round(num)
    num = round < 10 ? num.toFixed(2) : round < 100 ? num.toFixed(1) : round
    return `${num} ${'KMGTPEZY'[i-1]}B`
}

Here's some examples:

humanFileSize(0)          // "0 B"
humanFileSize(1023)       // "1023 B"
humanFileSize(1024)       // "1.00 KB"
humanFileSize(10240)      // "10.0 KB"
humanFileSize(102400)     // "100 KB"
humanFileSize(1024000)    // "1000 KB"
humanFileSize(12345678)   // "11.8 MB"
humanFileSize(1234567890) // "1.15 GB"

回答12:

1551859712 / 1024 = 1515488
1515488 / 1024 = 1479.96875
1479.96875 / 1024 = 1.44528198242188

Your solution is correct. The important thing to realize is that in order to get from 1551859712 to 1.5, you have to do divisions by 1000, but bytes are counted in binary-to-decimal chunks of 1024, hence why the Gigabyte value is less.

回答13:

I found @cocco's answer interesting, but had the following issues with it:

1. Don't modify native types or types you don't own
2. Write clean, readable code for humans, let minifiers optimize code for machines
3. (Bonus for TypeScript users) Doesn't play well with TypeScript

TypeScript:

 /**
 * Describes manner by which a quantity of bytes will be formatted.
 */
enum ByteFormat {
  /**
   * Use Base 10 (1 kB = 1000 bytes). Recommended for sizes of files on disk, disk sizes, bandwidth.
   */
  SI = 0,
  /**
   * Use Base 2 (1 KiB = 1024 bytes). Recommended for RAM size, size of files on disk.
   */
  IEC = 1
}

/**
 * Returns a human-readable representation of a quantity of bytes in the most reasonable unit of magnitude.
 * @example
 * formatBytes(0) // returns "0 bytes"
 * formatBytes(1) // returns "1 byte"
 * formatBytes(1024, ByteFormat.IEC) // returns "1 KiB"
 * formatBytes(1024, ByteFormat.SI) // returns "1.02 kB"
 * @param size The size in bytes.
 * @param format Format using SI (Base 10) or IEC (Base 2). Defaults to SI.
 * @returns A string describing the bytes in the most reasonable unit of magnitude.
 */
function formatBytes(
  value: number,
  format: ByteFormat = ByteFormat.SI
) {
  const [multiple, k, suffix] = (format === ByteFormat.SI
    ? [1000, 'k', 'B']
    : [1024, 'K', 'iB']) as [number, string, string]
  // tslint:disable-next-line: no-bitwise
  const exp = (Math.log(value) / Math.log(multiple)) | 0
  // or, if you'd prefer not to use bitwise expressions or disabling tslint rules, remove the line above and use the following:
  // const exp = value === 0 ? 0 : Math.floor(Math.log(value) / Math.log(multiple)) 
  const size = Number((value / Math.pow(multiple, exp)).toFixed(2))
  return (
    size +
    ' ' +
    (exp 
       ? (k + 'MGTPEZY')[exp - 1] + suffix 
       : 'byte' + (size !== 1 ? 's' : ''))
  )
}

// example
[0, 1, 1024, Math.pow(1024, 2), Math.floor(Math.pow(1024, 2) * 2.34), Math.pow(1024, 3), Math.floor(Math.pow(1024, 3) * 892.2)].forEach(size => {
  console.log('Bytes: ' + size)
  console.log('SI size: ' + formatBytes(size))
  console.log('IEC size: ' + formatBytes(size, 1) + '\n')
});

回答14:

For those who use Angular, there's a package called angular-pipes that has a pipe for this:

File

import { BytesPipe } from 'angular-pipes';

Usage

{{ 150 | bytes }} <!-- 150 B -->
{{ 1024 | bytes }} <!-- 1 KB -->
{{ 1048576 | bytes }} <!-- 1 MB -->
{{ 1024 | bytes: 0 : 'KB' }} <!-- 1 MB -->
{{ 1073741824 | bytes }} <!-- 1 GB -->
{{ 1099511627776 | bytes }} <!-- 1 TB -->
{{ 1073741824 | bytes : 0 : 'B' : 'MB' }} <!-- 1024 MB -->

Link to the docs.

回答15:

let bytes = 1024 * 10 * 10 * 10;

console.log(getReadableFileSizeString(bytes))

will return 1000.0Кб instead of 1MB