JavaScript Display Possibilities
JavaScript can "display" data in different ways:
- Writing into an HTML element, using innerHTML.
- Writing into the HTML output using document.write().
- Writing into an alert box, using window.alert().
- Writing into the browser console, using console.log().
Using innerHTML
To access an HTML element, JavaScript can use the document.getElementById(id) method.
The id attribute defines the HTML element. The innerHTML property defines the HTML content:
Example
<!DOCTYPE html>
<html>
<body>
<h1>My First Web Page</h1>
<p>My First Paragraph</p>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = 5 + 6;
</script>
</body>
</html>
Changing the innerHTML property of an HTML element is a common way to display data in HTML.
Using document.write()
For testing purposes, it is convenient to use document.write():
Example
<!DOCTYPE html>
<html>
<body>
<h1>My First Web Page</h1>
<p>My first paragraph.</p>
<script>
document.write(5 + 6);</script>
</body>
</html>
Using document.write() after an HTML document is fully loaded, will delete all existing HTML:
Example
<!DOCTYPE html>
<html>
<body>
<h1>My First Web Page</h1>
<p>My first paragraph.</p>
<button onclick="document.write(5 + 6)">Try it</button>
</body>
</html>
The document.write() method should only be used for testing.
Using window.alert()
You can use an alert box to display data:
Example
<!DOCTYPE html>
<html>
<body>
<h1>My First Web Page</h1>
<p>My first paragraph.</p>
<script>
window.alert(5 + 6);</script>
</body>
</html>
Using console.log()
For debugging purposes, you can use the console.log() method to display data.
You will learn more about debugging in a later chapter.
Example
<!DOCTYPE html>
<html>
<body>
<script>
console.log(5 + 6);</script>
</body>
</html>
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