JavaScript/Changing elements

On this page, we show how to change two different things of an HTML element, respectively, DOM node.

Its content (there is only one - or none)
Any of its attributes (there may be many)

Please take note of this distinction between content and attributes.

<!-- in general: -->
<element_name attribute_name="attribute_value">content of the element</element_name>
<!-- a concrete example. 'href' is an attribute. 'Visit IANA...' is the content. -->
<a href="https://www.example.com">Visit IANA's example domain.</a>

Example page

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We use the following example HTML page to demonstrate the possibilities.

<!DOCTYPE html>
<html>
<head>
 <script>
functionshow(){
"use strict";
// ...
}
</script>
</head>
<body id="body" style="margin:2em">
 <p id="p1" style="background: aqua">A blue paragraph</p>
 <svg id="svgSrc" width="100" height="100" viewBox="0 0 100 100">
 <circle cx="50" cy="50" r="25" fill="green"/>
 </svg>
 <p />
 <a id="refToSomewhere" href="https://www.example.com">Visit IANA's example domain.</a>
 <p />
 <button id="buttonShow" onclick="show()">Start</button>
</body>
</html>

Clicking on the button invokes the function show. The examples should be included there.

Change the content

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We use the example of a paragraph p. To change its content, the text, just assign the new value to its innerHTML.

functionshow(){
"use strict";
constelem=document.getElementById("p1");
elem.innerHTML="New text in the paragraph.";
}

Or, to do the same with a different HTML element, we change the SVG graphic.

functionshow(){
"use strict";
constelem=document.getElementById("svgSrc");
elem.innerHTML="<rect width='80' height='40' fill='blue'/>";
}

Because the new text is HTML code, you can 'misuse' this approach to add child nodes.

functionshow(){
"use strict";
constelem=document.getElementById("p1");
elem.innerHTML="New text in the paragraph.<p>next P</p><p>and even one more P</p>";
}

The script inserts two more paragraphs, but not behind the first one. They are within the first one.

<p id="p1">New text in the paragraph
 <p>next P</p>
 <p>and even one more P</p>
</p>

Change an attribute

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In general, the syntax to change attributes is as follows:

element_name.attribute_name="new value";
// or:
element_name.setAttribute("attribute_name","new value");

The HTML element a knows a href attribute: <a id="refToSomewhere" href="https://www.example.com">...</a>. This href attribute can be changed:

functionshow(){
"use strict";
constelem=document.getElementById("refToSomewhere");
elem.href="https://en.wikibooks.org";
elem.innerHTML="Link changed";
}

First, the element is located. Second, the function assigns a new value to its attribute 'href' (and to the innerHTML).

The following example changes the src attribute of img element and the value attribute of button element

// The HTML
<img id="imgOne" src="myPicture.jpg">
<input id="buttonOne" value="I'm a button!">
// The JavaScript
document.getElementById("imgOne").src = "otherPicture.jpg";
const b = document.getElementById("buttonOne");
b.value = "I'm a changed button";

setAttribute()

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The modification of attributes can also be done via the function setAttribute.

functionshow(){
"use strict";
constelem=document.getElementById("refToSomewhere");
elem.setAttribute("href","https://en.wikibooks.org");
elem.innerHTML="Link changed";
}