How to mock File in javascript?

Question

I'm developing some small project to exercise my TDD skills. The project consists of an audio player which has the ability to drag'n'drop files in a playlist. I'm using Jasmine as a testing framework. The problem I faced is that I can't mock javascript files to test my file upload functionality. I tried to create a File like this:

new File(new Blob(), "name");

but Chrome does not allow creating files manually. File's constructor is illegal to use. I found a solution with grunt.js which consists of returning some files from grunt, but I don't really wanna use server-side for such a small test project. Is there any workaround for this problem?

Answer 1

Chrome will let you create a new file:

var f = new File([""], "filename", { type: 'text/html' });

However IE11 (and other browsers?) will not.

Here's is my (poor?) fake File:

var blob = new Blob([""], { type: 'text/html' });
blob["lastModifiedDate"] = "";
blob["name"] = "filename";
var fakeF = blob;

You can fill in the values as you see fit. You can fill the blob with whatever you need. (See the other answer for how to use an image).

I've tested this in IE11, Chrome and Firefox. So far I seems to work, at least for my unit testing purposes.

Bonus: Here it is in typescript:

let blob = new Blob([""], { type: 'text/html' });
blob["lastModifiedDate"] = "";
blob["name"] = "filename";

let fakeF = <File>blob;

Answer 2

You don't need to create a blob, you can do this which applies the genuine image string directly (I used this converter), or you can do follow the example below (if you don't actually care about having a valid image]):

html <img id="test" />

var img = window.btoa('I don't care about a broken image');
document.getElementById('test').src='data:image/png;base64,'+img;

The btoa function is just to create base64 from a string.