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

newbie here. problem have written method checks uploaded file size , extension in order validate it. however, checking extensions not solution kind of validation may cause lot of problems. want check actual file type , validate without using extension method. have tried use jquery file validator no avail... snippet 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 larger 1mb!');                 }                 else {                     var reader = new filereader();                     reader.onload = imageisloaded;                     reader.readasdataurl(this.files[0]);                 }             } else alert('this not image file!');         });         function imageisloaded(e) {             result = e.target.result;             $('#image').attr('src', result);         };     }); 

it called once upload input changes , after validation uploads , displays image. now, care validation , or ideas appreciated!

try this:

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. }