JavaScript Output
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>
Try it Yourself »
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>
Try it Yourself »
Using document.write() after an HTML document is loaded, will delete all existing HTML:
Example
<!DOCTYPE html>
<html>
<body>
<h1>My First Web Page</h1>
<p>My first paragraph.</p>
<button type="button" onclick="document.write(5 + 6)">Try it</button>
</body>
</html>
Try it Yourself »
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>
Try it Yourself »
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>
Try it Yourself »
