FormData append key value is not working

Question

Can you tell me whats wrong with this   var formdata   new FormData    formdata append  key    value    console log formdata     My output looks like this  I cant find my  key  -  value  pair  FormData    proto    FormData   append  function append      native code       arguments  null    caller  null    length  0    name   append     prototype  append      proto    function Empty       constructor  function FormData      native code      arguments  null   caller  null   length  0   name   FormData    prototype  FormData   toString  function toString      native code       proto    Object     proto    Object     defineGetter    function   defineGetter        native code        defineSetter    function   defineSetter        native code        lookupGetter    function   lookupGetter        native code        lookupSetter    function   lookupSetter        native code      constructor  function Object      native code      hasOwnProperty  function hasOwnProperty      native code      isPrototypeOf  function isPrototypeOf      native code      propertyIsEnumerable  function propertyIsEnumerable      native code      toLocaleString  function toLocaleString      native code      toString  function toString      native code      valueOf  function valueOf      native code      I can t understand  Yesterday it worked so well  and today my head crashed the keyboard so many times  Firefox  Chrome  both the same

User · Answer

You say it s not working  What are you expecting to happen   There s no way of getting the data out of a FormData object  it s just intended for you to use to send data along with an XMLHttpRequest object  for the send method    Update almost five years later  In some newer browsers  this is no longer true and you can now see the data provided to FormData in addition to just stuffing data into it  See the accepted answer for more info

User · Answer

In my case on Edge browser      const formData   new FormData this form     for  const  key  value  of formData entries            formObject key    value        give me the same error  So I m not using FormData and i just manually build an object  import React from  react       import formDataToObject from  form-data-to-object           let formObject           EDGE compatibility -  replace FormData by for  let i   0  i  lt  this form length  i        if  this form i  name        formObject this form i  name    this form i  value         const data   formDataToObject toObj formObject      convert  user email    customer mail com    gt   user    email   customer mail com    const orderRes   await fetch   api orders             method   POST           credentials   same-origin           headers               Content-Type    application json                     body  JSON stringify data             const order   await orderRes json

User · Answer

You might have been having the same problem I was initially having  I was trying to use FormData to grab all my input files to upload an image  but at the same time I wanted to append a session ID to the information passed along to the server  All this time  I thought by appending the information  you would be able to see it in the server by accessing the object  I was wrong  When you append to FormData  the way to check the appended information on the server is by a simple   POST   your appended data    query  like so   js      form   submit function        var sessionID   8      var formData   new FormData this       formData append  id   sessionID          ajax           url   yoururl php           data  formData          processData  false          contentType  false          type   POST           success  function data               alert data                           then on php    sessionID     POST  id     files     FILES  image      foreach   files as  key  gt val

User · Answer

New in Chrome 50  and Firefox 39   resp  44      formdata entries    combine with Array from   for debugability  formdata get key  and more very useful methods   Original answer   What I usually do to  debug  a FormData object  is just send it  anywhere   and check the browser logs  eg  Chrome devtools  Network tab    You don t need a the same Ajax framework  You don t need any details  Just send it   var xhr   new XMLHttpRequest  xhr open  POST        true   xhr send data     Easy

User · Answer

form data doesn t appear in web browser console   for  var data of formData      console log data       try this way it will show

User · Answer

you can see it  you need to use console log formData getAll  your key     watch the  https   developer mozilla org en-US docs Web API FormData getAll

User · Answer

If you are in Chrome you can check the Post Data  Here is How to check the Post data   Go to Network Tab Look for the Link to which you are sending Post Data Click on it In the Headers  you can check Request Payload to check the post data

User · Answer

React Version  Make sure to have a header with  content-type    multipart form-data    handleSubmit e        e preventDefault        const formData   new FormData              formData append  file   this state file       const config           headers             content-type    multipart form-data                      axios post   upload   formData  config            then  resp    gt                 console log resp              catch  error    gt                   handleImageChange e        e preventDefault        let file   e target files 0       this setState         file  file               View     html   lt input className  form-control      type  file       onChange   e   gt this  handleImageChange e       gt

[javascript] FormData.append("key", "value") is not working

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