Preview Image before uploading

preview.js

$('#image-browse-button').change(function() {
  previewImage(this);
});

function previewImage(input) {
    if(input.files && input.files[0]) {
        var reader= new FileReader(),
            image = new Image();
        reader.onload = function(_file) {
            image.src = _file.target.result;
            image.onload = function(file) {
                var w = this.width,
                    h = this.height;
                    if (h < w)
                        w = w/h*250;
                    else 
                        w = 250;
                $('#avatar-preview img').attr('src',this.src).css("width", w);
            }
        }
        reader.readAsDataURL(input.files[0]);
    }
}