Why does javascript-jQuery + ajax File Upload fail?

Html: {code ...} backend php part: ajax. php {code ...} the js part is successfully uploaded using js, but there are two errors when using jquery: one is using $. ajax method: {code ...} the error message says the pic in $ _ FILES cannot be found. Why? Supplement: part of... html:

File Upload

Backend php part: ajax. php

The js part is successfully uploaded using js, but two errors occur when jquery is used:
One is to use the $. ajax method:

$(function(){        $(".sub").click(function(){             var fd=new FormData($("#up"));                    $.ajax({            url: 'ajax.php' ,            type: 'POST',            data: fd,            async: false,            cache: false,            contentType: false,           processData: false,            success: function (returndata) {                alert(returndata);            },            error: function (returndata) {                alert(returndata);            }       });              })})  

The error message says the pic in $ _ FILES cannot be found. Why?
Supplement: This is done. var fd = new FormData ($ ("# up"); it must be written:
Var fd = new FormData ($ ("# up") [0]);
Specific visible: http://segmentfault.com/q/1010000004213457
And http://segmentfault.com/a/1190000002938709

When using the $. post method:

$.post("ajax.php",fd,function(data){            console.log(data);         })

Error: Uncaught TypeError: Illegal invocation
Why?
(Jquery is in version 1.7.1)

Reply content:

Html section:

File Upload

Backend php part: ajax. php

The js part is successfully uploaded using js, but two errors occur when jquery is used:
One is to use the $. ajax method:

$(function(){        $(".sub").click(function(){             var fd=new FormData($("#up"));                    $.ajax({            url: 'ajax.php' ,            type: 'POST',            data: fd,            async: false,            cache: false,            contentType: false,           processData: false,            success: function (returndata) {                alert(returndata);            },            error: function (returndata) {                alert(returndata);            }       });              })})  

The error message says the pic in $ _ FILES cannot be found. Why?
Supplement: This is done. var fd = new FormData ($ ("# up"); it must be written:
Var fd = new FormData ($ ("# up") [0]);
Specific visible: http://segmentfault.com/q/1010000004213457
And http://segmentfault.com/a/1190000002938709

When using the $. post method:

$.post("ajax.php",fd,function(data){            console.log(data);         })

Error: Uncaught TypeError: Illegal invocation
Why?
(Jquery is in version 1.7.1)

Incorrect settings.

var data = new FormData();data.append('file', $('input[type=file]')[0].files[0]);$.ajax({        url: 'ajax.php',        data: data,        processData: false,        type: 'POST'        contentType: 'multipart/form-data',        mimeType: 'multipart/form-data',        success: function (data) {            alert(data);        }    });

Ajax cannot upload attachments. If you need to upload attachments, see use the jQuery form plug-in.

Ajax can only transmit text streams, but cannot transport binary files.

For more information, see what I wrote about FormData not refreshing uploaded files.

FormData

Ajax cannot upload files, and the enctype attribute of form upload files is required.

      contentType: false,       processData: false,