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Browser Developer Tools Tutorial

This tutorial will explain how to use the developer tools built in to your web browser.

Table of Contents

View source

View the HTML source of a web page.

Chrome

Firefox

Safari

Hard refresh

Portions of a page such as images and JavaScript source code are sometimes cached by the browser. If you change the source code or image, you need to tell your browser to reload it. This comic explains (credit: xkcd.com). refresh types

Developer tools

How to open the developer tools.

Chrome

Firefox

Safari

Console

Use the console to see errors generated while rendering a page. Also, anything sent to console.log() in JavaScript will appear in the console.

For example, create test.html with the following contents.

<html>
  <body>
    Hello world!
    <img src="bad.jpg" />
  </body>
</html>

Open test.html in your browser. Open the developer tools. Select the Console tab.

developer tools console

Elements AKA DOM

Use the Elements tab to link rendered parts of a page to the underlying HTML and CSS. This is the Document Object Model (DOM).

Create two files for this example, index.html and style.css.

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Hello world</title>
    <link rel="stylesheet" type="text/css" href="style.css" />
  </head>
  <body>
    <div class="important"><p>Hello</p></div>
    <div><p>world</p></div>
  </body>
</html>

style.css

div.important {
  font-weight: bold;
  font-size: 200%;
}

Open index.html in your browser. Open the developer tools. Select the Elements tab.

Click a line of HTML to see where it appears on the rendered page.

Use the selection tool to hover over a rendered part of the page and see the HTML behind it.

Cookies

To inspect cookies, you’ll need to open the developer tools for your browser first.

Open up a new tab and navigate to any news website (example here is the NY Times). Inspect the cookies. You can see attributes such as the name, value, domain, expiration date, and more about each cookie. Cookies whose domain matches the current page are first-party cookies, and those with a different domain are third-party cookies.

Chrome

Firefox

Safari

Private browsing

Private browsing mode creates a temporary session with separate cookies, browser history, etc. When you close all your private browsing tabs, the temporary information is removed.

Chrome “Incognito Window”

Firefox “Private Window”

Safari “Private Window”

JavaScript debugger

Project 3 JavaScript Debugging Tutorial

See the Project 3 React/JS Debugging Tutorial for tools for debugging Javascript with browser tools.