Uncaught TypeError: Cannot read property 'value' of null

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I'm getting error in this code, I'm trying to do an event where in when the page is load, it will do the event. But the problem is when I go to other function, but same page, it gets a error of null on that variable. It has no problem when I execute this codes, but when I'm on other part of my codes this error occurs.

Uncaught TypeError: Cannot read property 'value' of null

$(document).ready(function(){


      var str = document.getElementById("cal_preview").value;
      var str1 = document.getElementById("year").value;
      var str2 = document.getElementById("holiday").value;
      var str3 = document.getElementById("cal_option").value;


        if (str=="" && str1=="" && str2=="" && str3=="" )
          {
            document.getElementById("calendar_preview").innerHTML="";
              return;
            } 
          if (window.XMLHttpRequest)
          {// code for IE7+, Firefox, Chrome, Opera, Safari
            xmlhttp=new XMLHttpRequest();
          }
          else
          {// code for IE6, IE5
            xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
          }

          xmlhttp.onreadystatechange=function()
          {
            if (xmlhttp.readyState==4 && xmlhttp.status==200)
              {
                document.getElementById("calendar_preview").innerHTML=xmlhttp.responseText;
              }
          }

        var url = calendar_preview_vars.plugin_url + "?id=" + str +"&"+"y="+str1+"&"+"h="+str2+"&"+"opt="+str3;
        xmlhttp.open("GET",url,true);
        xmlhttp.send(); 


 });

I am unsure which of them is wrong because you did not provide your HTML, but one of these does not exist:

var str = document.getElementById("cal_preview").value;
var str1 = document.getElementById("year").value;
var str2 = document.getElementById("holiday").value;
var str3 = document.getElementById("cal_option").value;

There is either no element with the id cal_preview, year, holiday, cal_option, or some combination.

Therefore, JavaScript is unable to read the value of something that does not exist.

EDIT:

If you want to check that the element exists first, you could use an if statement for each:

var str,
element = document.getElementById('cal_preview');
if (element != null) {
    str = element.value;
}
else {
    str = null;
}

You could obviously change the else statement if you want or have no else statement at all, but that is all about preference.

Uncaught TypeError: Cannot read property of undefined , Out of the six primitive types defined in JavaScript, namely boolean, string, symbol, number, Null, and undefined, no other type throws as many errors as  Therefore, JavaScript is unable to read the value of something that does not exist. EDIT : If you want to check that the element exists first, you could use an if statement for each:

Easier and more succinct with || ...:

$(document).ready(function(){


  var str = ((document.getElementById("cal_preview")||{}).value)||"";
  var str1 = ((document.getElementById("year")||{}).value)||"";
  var str2 = ((document.getElementById("holiday")||{}).value)||"";
  var str3 = ((document.getElementById("cal_option")||{}).value)||"";


    if (str=="" && str1=="" && str2=="" && str3=="" )
      {
        document.getElementById("calendar_preview").innerHTML="";
          return;
        } 
      if (window.XMLHttpRequest)
      {// code for IE7+, Firefox, Chrome, Opera, Safari
        xmlhttp=new XMLHttpRequest();
      }
      else
      {// code for IE6, IE5
        xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
      }

      xmlhttp.onreadystatechange=function()
      {
        if (xmlhttp.readyState==4 && xmlhttp.status==200)
          {
            document.getElementById("calendar_preview").innerHTML=xmlhttp.responseText;
          }
      }

    var url = calendar_preview_vars.plugin_url + "?id=" + str +"&"+"y="+str1+"&"+"h="+str2+"&"+"opt="+str3;
    xmlhttp.open("GET",url,true);
    xmlhttp.send(); 


});

​​Avoiding those dang cannot read property of undefined errors , Uncaught TypeError: Cannot read property 'foo' of undefined.​ The dreaded error we all hit at some point in JavaScript development. Could be  Uncaught TypeError: Cannot read property 'innerHTML' of null All this means is that you are trying to access a property of an object that is undefined. These usually happens when we don't test an object before using it.

Add a check

if (document.getElementById('cal_preview') != null) {
    str = document.getElementById("cal_preview").value;
}

Uncaught TypeError: Cannot read property 'value' of undefined , Seems like one of your values, with a property key of 'value' is undefined. Test that i1 , i2 and __i are defined before executing the if statements: Uncaught TypeError: Cannot read property 'map' of undefined with React Tag: javascript , reactjs I have implemented a little test application in React to fetch data via AJAX, but it is not working as inteded, hence i get following error:

My mistake was that I was keeping the Javascript file ( tag) above the html declaration.

It worked by placing the js script tag at the bottom of the body inside the body. (I did not the script on load of the page.)

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Instead of document or $(document) to avoid JQuery, you can add a TimeOut to validate the objects. TimeOut is executed after loading all objects within the page and other events...

setTimeout(function () { 

var str = document.getElementById("cal_preview").value;
var str1 = document.getElementById("year").value;
....
....
....

}, 0);

Uncaught TypeError: Cannot read property of null, This will result in Uncaught TypeError: Cannot read property 'value' of null . The reason will be that the element with id input does not exist. Uncaught TypeError: Cannot read property 'local' of undefined in chrome extension. I have written a Chrome extension. I cannot use localStorage.setItem and localStorage.getItem for storing and retrieving because background and browser action runs in different environment [as seen here].

TypeError: Cannot read property 'firstName' of undefined , I keep getting "TypeError: Cannot read property 'firstName' of undefined" and I cannot figure out what is going on. Does anyone have an idea? var bob = { Dismiss Join GitHub today. GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.

Uncaught TypeError: Cannot read property 'source' of undefined , Hi all, I am building my WikiPedia Viewer but I have this issue: On this line: I do not get it? Here is my project:  Uncaught TypeError: Cannot read property 'version' of undefined #20291. Closed divyanshk7 opened this issue Jan 3, 2020 · 1 comment Closed

Uncaught TypeError: Cannot read property 'raw' of undefined · Issue , js for the elasticsearch field and fillter. I got this error when start typing in the search box: `Autocomplete.js:74 Uncaught TypeError: Cannot read  I recently enabled the bundled tags flag on all tags in our website to reduce the number of request sent from the browser to Tealium and also mimified the tag templates. The change worked perfectly, however after making a few other changes to the Criteo - OneTag, I have started to get the following

Comments
  • where is your "calendar_preview_vars" ?
  • Please post your accompanying HTML
  • you sure the elements with first four ids exist? put a debugger; statement in your ready function and see which line throws error.
  • They do exist, it has no problem when this function is called, but when you are on other function, this is the time that it has error.
  • If document.getElementById can't find an element with the supplied ID, it returns null. So the error is telling you it can't find one of the elements by ID.
  • I think your getting my point, I tried to put a validation there like if null, but did not work. Is it possible to verify if value exist or not? Did I understand it correctly?
  • You want to just check if it exists and do nothing if it does not or try to figure out which one it thinks does not exist?
  • I want to check if all of them exist, if not skip the process.
  • the error now is on this part document.getElementById("calendar_preview").innerHTML=xmlhttp.responseText;,. cannot set property innerhtml of null
  • Just simply do exactly the same that you did on the previous. Also, if you want, you could just skip everything if one of them does not exist.