How to Print Output in JavaScript: Simple Guide

To print output in JavaScript, use console.log() to show messages in the browser console or terminal. You can also use alert() to show popup messages or document.write() to write directly to the webpage.

Syntax

The most common way to print output in JavaScript is using console.log(). It takes one or more values inside parentheses and prints them to the console.

Other methods include alert() which shows a popup message, and document.write() which writes directly to the webpage.

javascript

console.log(value1, value2, ...);
alert(message);
document.write(content);

Example

This example shows how to print text and numbers using console.log(), display a popup with alert(), and write text on the webpage with document.write().

javascript

console.log('Hello, world!');
console.log('Sum:', 5 + 3);
alert('This is a popup message!');
document.write('This text is written on the webpage.');

Output

Hello, world!
Sum: 8
(This shows a popup with message)
(This writes text on the webpage)

Common Pitfalls

One common mistake is forgetting to open the browser console to see console.log() output. Another is using document.write() after the page loads, which can overwrite the whole page.

Also, alert() stops the page until you click OK, so use it sparingly.

javascript

/* Wrong: document.write after page load */
window.onload = function() {
  document.write('This will erase the page content!');
};

/* Right: Use console.log instead */
window.onload = function() {
  console.log('Page loaded');
};

Quick Reference

Method	Description	Where Output Appears
console.log()	Prints messages to the browser console or terminal	Browser Console / Terminal
alert()	Shows a popup alert box with a message	Popup dialog on webpage
document.write()	Writes text directly into the webpage HTML	Webpage content area

Key Takeaways

Use console.log() to print messages to the browser console for debugging.

alert() shows popup messages but pauses page interaction until dismissed.

Avoid using document.write() after the page loads to prevent overwriting content.

Open the browser console (F12 or Ctrl+Shift+I) to see console.log output.

Choose the output method based on whether you want console, popup, or page display.