Javascript File size validation without File API

You can use a polyfill to add support for File API in older browsers such as IE8 and IE9.

Go here and scroll down to the "File API" section.

https://github.com/Modernizr/Modernizr/wiki/HTML5-Cross-Browser-Polyfills

You can do this using Javascript as shown below,

    $('input[type="file"]').change(function () {
    if (this.files[0] != undefined) {
        var name = this.name;
        var filesize = this.files[0].size;
        var field = $('#' + this.name).parents('.input-group');

        //check if file size is larger than 3MB(which is 3e+6 bytes)
        if (filesize > 3000000) {
           alert(filesize);
        //reset that input field if its file size is more than 3MB
           $('[name="' + name + '"]').val('')
        }
    }
});

you can just include this for all input of type='file' by changing size limit in bytes.

Active X (haters gonna hate):

var filepath = 'path/to/file',
    fso = new ActiveXObject('Scripting.FileSystemObject'),
    file = fso.getFile(filepath),
    imgbytes = file.size;

console.log(imgbytes);

Not that I know. Anyway, as client validation is only for user-friendlyness purposes, you could easilly fall back to a check on the server if your user doesn't have a browser supporting file API. With old browsers they should be used to get less user-friendly sites anyway...