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JavaScript Output


JavaScript does NOT have any built-in print or display functions.


JavaScript Display Possibilities

JavaScript can "display" data in different ways:

  • Writing into an alert box, using window.alert().
  • Writing into the HTML output using document.write().
  • Writing into an HTML element, using innerHTML.
  • Writing into the browser console, using console.log().

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 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 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>
Try it Yourself »

The document.write() method should only be used for testing.


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 »

To "display data" in HTML, (in most cases) you will set the value of an innerHTML property.


Using console.log()

In your browser, you can use the console.log() method to display data.

Activate the browser console with F12, and select "Console" in the menu.

Example

<!DOCTYPE html>
<html>
<body>

<h1>My First Web Page</h1>
<p>My first paragraph.</p>

<script>
console.log(5 + 6);
</script>

</body>
</html>
Try it Yourself »