JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <fieldset>
        <legend>Image upload</legend>
        <input type="file" onchange="getImg(this,500,'jpeg|png')" />
    </fieldset>
</form>

JavaScript

function getImg(input,max,accepted){
	var upImg=new Image(),test,size,msg=input.form;
	msg=msg.elements[0].children[0];
    return input.files?validate():
	(upImg.src=input.value,upImg.onerror=upImg.onload=validate);
        "author: b.b. Troy III p.a.e";
	function validate(){
		test=(input.files?input.files[0]:upImg);
		size=(test.size||test.fileSize)/1024;
		mime=(test.type||test.mimeType);

	mime.match(RegExp(accepted,'i'))?
	size>max?(input.form.reset(),msg.innerHTML=max+"KB Exceeded!"):
	msg.innerHTML="Upload ready...":	
	(input.form.reset(),msg.innerHTML=accepted+" file type(s) only!")
	}
}