jQuery how to check if uploaded file is an image without checking extensions?

Question

Newbie here. The problem is that I currently have written a method which checks uploaded file size and extension in order to validate it. However, checking extensions is not a solution as that kind of validation may cause a lot of problems. What I want to do is to check the actual file type and validate it without using extension method. I have tried to use jQuery file validator but to no avail... This is a snippet from my current code:

<input type='file' id='imageLoader' name='imageLoader' accept="image/*" data-type='image' />

Script:

App.Dispatcher.on("uploadpic", function() {         
        $(":file").change(function() {
            if (this.files && this.files[0] && this.files[0].name.match(/\.(jpg|jpeg|png|gif)$/) ) {
                if(this.files[0].size>1048576) {
                    alert('File size is larger than 1MB!');
                }
                else {
                    var reader = new FileReader();
                    reader.onload = imageIsLoaded;
                    reader.readAsDataURL(this.files[0]);
                }
            } else alert('This is not an image file!');
        });
        function imageIsLoaded(e) {
            result = e.target.result;
            $('#image').attr('src', result);
        };
    });

It is called once the upload input changes and after validation it uploads and displays the image. For now, I only care about validation and any help or ideas would be greatly appreciated!

Answer 1

Try something like this:

JavaScript

const file = this.files[0];
const  fileType = file['type'];
const validImageTypes = ['image/gif', 'image/jpeg', 'image/png'];
if (!validImageTypes.includes(fileType)) {
    // invalid file type code goes here.
}

jQuery

var file = this.files[0];
var fileType = file["type"];
var validImageTypes = ["image/gif", "image/jpeg", "image/png"];
if ($.inArray(fileType, validImageTypes) < 0) {
     // invalid file type code goes here.
}

Answer 2

You don't need jquery here.

var mimeType=this.files[0]['type'];//mimeType=image/jpeg or application/pdf etc...


//ie image/jpeg will be ['image','jpeg'] and we keep the first value
    if(mimeType.split('/')[0] === 'image'){
       console.log('the file is image');
    }

You can also create a function to check when a file is image.

function isImage(file){
   return file['type'].split('/')[0]=='image');//returns true or false
}

 isImage(this.file[0]);

Update (es6)

using es6 includes method, makes it even more simple.

const isImage = (file) => file['type'].includes('image');

Answer 3

Pls refer a related query here. The answer here suggests to load the image in an Image object and check for it's width and height properties to be non zero. I think the technique can be used to solve your problem too.

I also worked out a fiddle for you to refer. Pertinent code below:

var img = new Image();
img.addEventListener("load",function(){
  alert('success');
});
img.addEventListener("error",function(){
      alert('error');
});
  img.src = picFile.result;