Uncaught TypeError Cannot read property appendChild of null

Question

I m getting the following error     Uncaught TypeError  Cannot read property  appendChild  of null      myRequest onreadystatechange   script js 20   with my following code     index html   lt html gt       lt head gt           lt title gt Simple Page lt  title gt       lt  head gt       lt body gt           lt div id  mainContent  gt               lt h1 gt This is an AJAX Example lt  h1 gt           lt  div gt           lt script type  text javascript  src  script js  gt  lt  script gt       lt  body gt   lt  html gt    And here is my JavaScript file     script js    1  Create the request  var myRequest      feature check  if window XMLHttpRequest       Firefox  Safari     myRequest   new XMLHttpRequest      else if  window ActiveXObject      IE     myRequest   new ActiveXObject  Microsoft XMLHTTP           2  Create an event handler for our request to call back  myRequest onreadystatechange   function         console log  We were called         console log myRequest readyState       if myRequest readyState     4           var p   document createElement  p            var t   document createTextNode myRequest responseText           p appendChild t           document getElementById  mainContent   appendChild p                3  open and send it myRequest open  GET   simple txt   true       any parameters  myRequest send null     And here is the contents of simple txt     This is the contents of a simple text file    I put the script tag at the bottom of the html as suggested by  Tejs here but I m still getting this error

User · Answer

Use querySelector insted of getElementById     var c   document querySelector   mainContent        c appendChild document createElement  div

User · Answer

For people who have the same issue of querySelector or getElementById that returns the following error   Uncaught TypeError  Cannot read property  appendChild  of null   but you have a class name or id in the HTML     If your script tag is in the head  the JavaScript is loaded before your HTML  You will need to add defer to your script like so    lt script src  script js  defer gt  lt  script gt

User · Answer

add your script tag on the bottom of the body tag  so that script loads after html content then you won t get such error and add

User · Answer

Instead of using your script tag defining the source of your  js file in  lt head gt   place it at the bottom of your HTML code

User · Answer

There isn t an element on your page with the id  mainContent  when your callback is being executed   In the line   document getElementById  mainContent   appendChild p     the section document getElementById  mainContent   is returning null

User · Answer

You can load your External JS files in Angular and you can load them directly instead of defining in index html file   component ts   ngOnInit         this loadScripts          loadScripts         const dynamicScripts             scripts to be loaded        assets lib js hand-1 3 8 js          assets lib js modernizr jr js          assets lib js jquery-2 2 3 js          assets lib js jquery-migrate-1 4 1 js          assets js jr utils js             for  let i   0  i  lt  dynamicScripts length  i            const node   document createElement  script          node src   dynamicScripts i         node type    text javascript         node async   false        document getElementById  scripts   appendChild node               component html    lt div id  scripts  gt   lt  div gt    You can also load styles similarly   component ts   ngOnInit         this loadStyles          loadStyles         const dynamicStyles             styles to be loaded        assets lib css ui css          assets lib css material-theme css          assets lib css custom-style css             for  let i   0  i  lt  dynamicStyles length  i            const node   document createElement  link          node href   dynamicStyles i         node rel    stylesheet         document getElementById  styles   appendChild node               component html    lt div id  styles  gt   lt  div gt

User · Answer

put your javascript at the bottom of the page  ie after the element getting defined

User · Answer

those getting querySelector or getElementById that returns the following error  Uncaught TypeError  Cannot read property  appendChild  of null  or any other property  even if you have a class name or id in the HTML don t use  defer as it is too much browser dependent    lt script src  quot script js quot  defer gt  lt  script gt     don t use this  instead  put all your code in  script js  inside   document  ready function          your script here

User · Answer

If this is happening to you in an AJAX post  you ll want to compare the values that you re sending and the values that the Controller is expecting  In my case  I had changed a parameter in a serializable class from State to StateID  and then in an AJAX call didn t change the receiving field out  data  success  function  data    MakeAddressForm formData StateID   data State  Note that the class was changed - it doesn t matter what I call it in the formData  This created a null reference in the formData which I was trying to post back to the Controller once I d done the update   Obviously  if someone changed the state  which was the purpose of the form  then they didn t get the error  so it made for a hard one to find  This also through a 500 error   I m posting this here in hopes it saves someone else the time I ve wasted

User · Answer

Had the same problem when Load external  without cache using Javascript Load external  lt script gt  without cache using Javascript Had a good solution for  cache problem here  https   www c-sharpcorner com article how-to-force-the-browser-to-reload-cached-js-css-files-to-reflect-latest-chan  But this happend  Uncaught TypeError  Cannot read property  appendChild  of null  Here is good explanation  https   stackoverflow com a 58824439 14491024 As it said your script tag is in the head  the JavaScript is loaded before your HTML   In  Visual Studio by C  this problem is solved like this by adding Guid    Here is how it looks in the View page source

User · Answer

Nice answers here  I encountered the same problem  but I tried  lt script src  script js  defer gt  lt  script gt  but I didn t work quite well  I had all the code and links set up fine  The problem is I had put the js file link in the head of the page  so it was loaded before the DOM was loaded  There are 2 solutions to this    Use     window onload        gt          write your code here       Add the  lt script src  script js  gt  lt  script gt  to the bottom of the html file so that it loads last

[javascript] Uncaught TypeError: Cannot read property 'appendChild' of null

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