Format file size in bytes to human-readable string

format-file-size.js

function fileSizeFormat( num_bytes ) {
    if ( ! num_bytes ) return '0 bytes';
    typeof num_bytes == 'number' || ( num_bytes = parseFloat( num_bytes ) );
    if ( isNaN( num_bytes ) ) return '';

    var i = -1;
    var byteUnits = [ 'kB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
    do {
        num_bytes = num_bytes / 1000;
        i++;
    } while ( num_bytes > 999 && i < byteUnits.length - 1 );

    return ( num_bytes == Math.floor(num_bytes) ? num_bytes :
             Math.max( num_bytes, 0.1 ).toFixed( 1 ) ) +
}

specs.js

// Jasmine specs

describe( 'fileSizeFormat', function() {
    it(' should convert to appropriate unit', function() {
        var base = 1.3, i,
            byteUnits = [ 'kB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];

        for( i=1; i<=byteUnits.length; i++ ) {
            expect( fileSizeFormat( 1.3 * Math.pow( 1024, i ) ) )
                .toBe( base + ' ' + byteUnits[i - 1] );
        }
    });

    it('should parse float if argument is a string', function() {
        expect( fileSizeFormat( '1000' ) ).toBe( '1 kB' );
    });

    it('should work for 0', function() {
        expect( fileSizeFormat( 0 ) ).toBe( '0 bytes' );

    });

    it('should work for too large numbers', function() {
        expect( fileSizeFormat( 1.3 * Math.pow( 1000, 9 ) ) ).toBe( 1.3 * 1024 + ' YB' );

    });
});