What is the reason behind getElementsByClassName not functioning while getElementById is working perfectly?

Question

What is the reason behind getElementsByClassName not functioning while getElementById is working perfectly?

The initial code snippet is not functioning correctly

DN.onkeyup = DN.onkeypress = function(){
  var div = document.getElementById("DN").value
  document.document.getElementsByClassName("options-parameters-input").style.fontSize = div;
}

#one{
    height:100px;
    width:100px;
    background-color:#CCCCCC;
    border:none;
    margin:10px;
    float:left;
}

<div id="one">
  <div class="options-parameters-input">
    gfdgd
  </div>
</div>
<br /><br /><br /><br /><br /><br /><br />
<table width="750" border="1" cellspacing="3" style="float:left;">
  <tr>
    <td>Test</td>
    <td><textarea id="DN"></textarea></td>
  </tr>
</table>

http://jsfiddle.net/gxTuG/85/

On the other hand, this piece of code is operational

DN.onkeyup = DN.onkeypress = function(){
  var div = document.getElementById("DN").value
  document.getElementById("one").style.fontSize = div;
}

#one{
    height:100px;
    width:100px;
    background-color:#CCCCCC;
    border:none;
    margin:10px;
    float:left;
}

<div id="one">gfdgd</div>
<br /><br /><br /><br /><br /><br /><br />
<table width="750" border="1" cellspacing="3" style="float:left;">
  <tr>
    <td>Test</td>
    <td><textarea id="DN"></textarea></td>
  </tr>
</table>

http://jsfiddle.net/gxTuG/86/

In the first code block, an attempt was made to use getElementsByClassName, but it resulted in an error...

Error: Uncaught TypeError: Cannot read property 'getElementsByClassName' of undefined(…)

Hence, the question arises on how to successfully target elements by their class names?

The objective is to enable administrators to modify or introduce new CSS rules for specific HTML elements via textarea or input fields, such as

.

Is this approach deemed effective for injecting new CSS rules?

Thank you

javascript jquery html css

Answer 1

Answer №1

It is recommended to use addEventListener() in this scenario. First, declare with DN, then call the value of DN using this.value. This allows for the same function within the element.
To target the ClassName, use
document.getElementsByClassName("options-parameters-input")[0]
and end with [0]. As classes can match multiple elements, [0] identifies the first one that matches.
The font size in the Dom should be specified with px.

var DN = document.getElementById("DN");
DN.addEventListener("keyup",both);

function both(){
document.getElementsByClassName("options-parameters-input")[0].style.fontSize = this.value+'px';
}

#one{
    height:100px;
    width:100px;
    background-color:#CCCCCC;
    border:none;
    margin:10px;
    float:left;
}

<div id="one">
<div class="options-parameters-input">
gfdgd
</div>
</div>
<br /><br /><br /><br /><br /><br /><br />
<table width="750" border="1" cellspacing="3" style="float:left;">
  <tr>
    <td>Test</td>
    <td><textarea id="DN"></textarea></td>
  </tr>
</table>

Answer 2

It is recommended to use addEventListener() in this scenario. First, declare with DN, then call the value of DN using this.value. This allows for the same function within the element.
To target the ClassName, use
document.getElementsByClassName("options-parameters-input")[0]
and end with [0]. As classes can match multiple elements, [0] identifies the first one that matches.
The font size in the Dom should be specified with px.

var DN = document.getElementById("DN");
DN.addEventListener("keyup",both);

function both(){
document.getElementsByClassName("options-parameters-input")[0].style.fontSize = this.value+'px';
}

#one{
    height:100px;
    width:100px;
    background-color:#CCCCCC;
    border:none;
    margin:10px;
    float:left;
}

<div id="one">
<div class="options-parameters-input">
gfdgd
</div>
</div>
<br /><br /><br /><br /><br /><br /><br />
<table width="750" border="1" cellspacing="3" style="float:left;">
  <tr>
    <td>Test</td>
    <td><textarea id="DN"></textarea></td>
  </tr>
</table>

Answer 3

Answer №2

When using getElementsByClassName, it returns an array of objects even if you only have one in your HTML document. Therefore, you need to use

getElementsByClassName("options-parameters-input")[0]

or adjust the index accordingly.

Answer 4

When using getElementsByClassName, it returns an array of objects even if you only have one in your HTML document. Therefore, you need to use

getElementsByClassName("options-parameters-input")[0]

or adjust the index accordingly.

Answer 5

Answer №3

document.getElementsByClassName can be used to target all elements with a specific class name. To manipulate a specific element, you will need to provide the index of that element in the collection. It is important to note that the method is actually called getElement__s__ByClassName. Remember this distinction.

For instance: HTML:

<div class="my-class>1st div</div>
<div class="my-class>2nd div</div>

JS:

let myDivs = document.getElementsByClassName("my-class");
myDivs[0].style.fontSize = '10px';

Answer 6

document.getElementsByClassName can be used to target all elements with a specific class name. To manipulate a specific element, you will need to provide the index of that element in the collection. It is important to note that the method is actually called getElement__s__ByClassName. Remember this distinction.

For instance: HTML:

<div class="my-class>1st div</div>
<div class="my-class>2nd div</div>

JS:

let myDivs = document.getElementsByClassName("my-class");
myDivs[0].style.fontSize = '10px';

What is the reason behind getElementsByClassName not functioning while getElementById is working perfectly?

Answer №1

Answer №2

Answer №3

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