Question

[Solved] Javascript Get Element by Id and set the value

I have a javascript function to which I pass a parameter. The parameter represents the id of an element (a hidden field) in my web page. I want to change the value of this element.

function myFunc(variable){
  var s= document.getElementById(variable);
  s.value = 'New value'
}

When I do this, I get an error that the value cannot be set because the object is null. But I know the object is not null because I see it in the html code generated by the browser.
Anyways, I tried the following code to debug

function myFunc(variable){
  var x = variable;
  var y  = 'This-is-the-real-id'
  alert(x + ', ' + y)
  var s= document.getElementById(x);
  s.value = 'New value'
}

When the alert message shows up, both parameters are the same, but I still get the error. But everything works fine when I do

  var s= document.getElementById('This-is-the-real-id');
  s.value = 'New value'

How can I fix this please

EDIT

The element for which I am setting the value is hidden field and the id is det dynamically, as the page loads. I have tried added this in the $(document).ready function but did not work

Enquirer: jpo

||

Solution #1:

If myFunc(variable) is executed before textarea is rendered to page, you will get the null exception error.

<html>
    <head>
    <title>index</title>
    <script type="text/javascript">
        function myFunc(variable){
            var s = document.getElementById(variable);
            s.value = "new value";
        }   
        myFunc("id1");
    </script>
    </head>
    <body>
        <textarea id="id1"></textarea>
    </body>
</html>
//Error message: Cannot set property 'value' of null 

So, make sure your textarea does exist in the page, and then call myFunc, you can use window.onload or $(document).ready function.
Hope it’s helpful.

Respondent: Xiaodan Mao

Solution #2:

Given

<div id="This-is-the-real-id"></div>

then

function setText(id,newvalue) {
  var s= document.getElementById(id);
  s.innerHTML = newvalue;
}    
window.onload=function() { // or window.addEventListener("load",function() {
  setText("This-is-the-real-id","Hello there");
}

will do what you want


Given

<input id="This-is-the-real-id" type="text" value="">

then

function setValue(id,newvalue) {
  var s= document.getElementById(id);
  s.value = newvalue;
}    
window.onload=function() {
  setValue("This-is-the-real-id","Hello there");
}

will do what you want

Respondent: mplungjan

Solution #3:

<html>
<head>
<script>
function updateTextarea(element)
{
document.getElementById(element).innerText = document.getElementById("ment").value;
}
</script>
</head>
<body>

<input type="text" value="Enter your text here." id = "ment" style = " border: 1px solid grey; margin-bottom: 4px;"  

onKeyUp="updateTextarea('myDiv')" />

<br>

<textarea id="myDiv" ></textarea>

</body>
</html>
Respondent: Dah Moymy

Solution #4:

For each element type, you can use specific attribute to set value. E.g.:

<div id="theValue1"></div>
window.document.getElementById("theValue1").innerText = "value div";

<input id="theValue2"></input>
window.document.getElementById("theValue2").value = "value input";

You can try example here!

Respondent: Darlan D.

Solution #5:

try like below it will work…

<html>
<head>
<script>
function displayResult(element)
{
document.getElementById(element).value = 'hi';
}
</script>
</head>
<body>

<textarea id="myTextarea" cols="20">
BYE
</textarea>
<br>

<button type="button" onclick="displayResult('myTextarea')">Change</button>

</body>
</html>
Respondent: Pandian

Solution #6:

I think the problem is the way you call your javascript function. Your code is like so:

<input type="button" onclick="javascript: myFunc(myID)" value="button"/>

myID should be wrapped in quotes.

Respondent: K.I

Solution #7:

Coming across this question,
no answer brought up the possibility of using .setAttribute() in addition to .value()

document.getElementById('some-input').value="1337";
document.getElementById('some-input').setAttribute("value", "1337");

Though unlikely helpful for the original questioner,
this addendum actually changes the content of the value in the pages source,
which in turn makes the value update form.reset()-proof.

I hope this may help others.

(Or me in half a year when I’ve forgotten about js quirks…)

Respondent: Aiyion.Prime

The answers/resolutions are collected from stackoverflow, are licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0 .

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