Cannot read property addEventListener of null

Question

I have to use vanilla JavaScript for a project   I have a few functions  one of which is a button that opens a menu   It works on pages where the target id exists  but causes an error on pages where the id doesn t exist   On those pages where the function cannot find the id  I receive a  Cannot read property  addEventListener  of null   error and none of my other functions work   Below is the code for the button that opens the menu    function swapper     toggleClass document getElementById  overlay     open       var el   document getElementById  overlayBtn    el addEventListener  click   swapper  false    var text   document getElementById  overlayBtn    text onclick   function    this innerHTML    this innerHTML      Menu      Close     Menu   return false       How do I deal with this  I probably need to all wrap this code in another function or use an if else statement so that it only searches for the id on specific pages  but not sure exactly

User · Answer

I was getting the same error  but performing a null check did not seem to help   The solution I found was to wrap my function inside an event listener for the whole document to check when the DOM finished loading   document addEventListener  DOMContentLoaded   function          el addEventListener  click   swapper  false         I think this is because I am using a framework  Angular  that is changing my HTML classes and ID s dynamically

User · Answer

script is loading before body  keep script after content

User · Answer

Add all event listeners when a window loads Works like a charm no matter where you put script tags   window addEventListener  load   startup    function startup        document getElementById  el   addEventListener  click   myFunc     document getElementById  el2   addEventListener  input   myFunc       myFunc

User · Answer

Put script at the end of body tag    lt html gt       lt body gt                             lt script src  main js  gt  lt  script gt       lt  body gt   lt  html gt

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I think the easiest approach would be to just check that el is not null before adding an event listener   var el   document getElementById  overlayBtn    if el     el addEventListener  click   swapper  false

User · Answer

I faced a similar situation  This is probably because the script is executed before the page loads  By placing the script at the bottom of the page  I circumvented the problem

User · Answer

Thanks from all  Load the Scripts in specific pages that you use  not for all pages  sometimes using swiper js or other library it may cause this error message  the only way to solve this issue it to load the JS library on specific pages that ID is exist and prevent loading of the same library in all pages   Hope this help you

User · Answer

It s just bcz your JS gets loaded before the HTML part and so it can t find that element  Just put your whole JS code inside a function which will be called when the window gets loaded   You can also put your Javascript code below the html

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I ve a collection of quotes along with names  I m using update button to update the last quote associated with a specific name  but on clicking update button it s not updating  I m including code below for server js file and external js file  main js    main js  external js   var update   document getElementById  update    if  update   update addEventListener  click   function         fetch  quotes       method   put     headers    Content-Type    application json      body  JSON stringify        name    Muskan        quote    I find your lack of faith disturbing          var update   document getElementById  update    if  update   update addEventListener  click   function         fetch  quotes       method   put     headers    Content-Type    application json      body  JSON stringify        name    Muskan        quote    I find your lack of faith disturbing            then res   gt       if res ok  return res json       then data   gt       console log data       window location reload true             server js file  app put   quotes    req  res    gt      db collection  quotations   findOneAndUpdate  name   Vikas          set           name  req body name          quote  req body quote                 sort    id  -1       upsert  true      err  result    gt       if  err  return res send err       res send result

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Thanks to  Rob M  for his help  This is what the final block of code looked like   function swapper       toggleClass document getElementById  overlay     open       var el   document getElementById  overlayBtn    if  el     el addEventListener  click   swapper  false      var text   document getElementById  overlayBtn      text onclick   function        this innerHTML    this innerHTML      Menu      Close     Menu       return false

User · Answer

I encountered the same problem and checked for null but it did not help  Because the script was loading before page load  So just by placing the script before the end body tag solved the problem

User · Answer

As others have said problem is that script is executed before the page  and in particular the target element  is loaded   But I don t like the solution of reordering the content   Preferred solution is to put an event handler on page onload event and set the Listener there  That will ensure the page and the target element is loaded before the assignment is executed  eg       lt script gt      function onLoadFunct                   set Listener here  also using suggested test for null                     lt  script gt        lt body onload  onLoadFunct         gt

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It seems that document getElementById  overlayBtn    is returning null because it executes before the DOM fully loads   If you put this line of code under  window onload function      -- put your code here     then it will run without issue   Example   window onload function        var mb   document getElementById  b        mb addEventListener  click   handler       mb addEventListener  click   handler2       function handler            p   html   lt br gt        p   text       lt br gt You clicked me-1  lt br gt        function handler2            p   html   lt br gt        p   text       lt br gt You clicked me-2  lt br gt

User · Answer

I simply added  async  to my script tag  which seems to have fixed the issue  I m not sure why  if someone can explain  but it worked for me  My guess is that the page isn t waiting for the script to load  so the page loads at the same time as the JavaScript      Async Await enables us to write asynchronous code in a synchronous fashion   it   s just syntactic sugar using generators and yield statements to    pause    execution  giving us the ability to assign it to a variable   Here s reference link- https   medium com siliconwat how-javascript-async-await-works-3cab4b7d21da

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This is because the element hadn t been loaded at the time when the bundle js was being executed   I d move the  lt script src  sample js  type  text javascript  gt  lt  script gt  to the very bottom of the index html file  This way you can ensure script is executed after all the html elements have been parsed and rendered

User · Answer

I had the same problem  but my id was present  So I tried adding  window onload   init   Then I wrapped my original JS code with an init function  call it what you want   This worked  so at least in my case  I was adding an event listener before my document loaded  This could be what you are experiencing as well

[javascript] Cannot read property 'addEventListener' of null

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