03: Devtools

21 tips

Design mode: you can edit text directly in the website by running this code in the console:
```
document.designMode = "on";
```
** $0**: The variable `$ 0` refers to the last element you selected in the elements tab.
Ctrl + shift + P: opens up command pallete so you can find commands and options easier.
built-in JQUery : The $(selector) function is built into chrome devtools, and is a much more concise way of doing document.querySelector(selector).
- $('h1') : equivalent of document.querySelector('h1')
- $$('h1') : equivalent of document.querySelectorAll('h1')
vizbug extension : allows you to visually design your website.
coverage: Open up the coverage tab in devtools to see how much javascript and css is used and unused. You can optimize your bundle with the info from this page.
live expressions: Use live expressions to keep track of a variable across the lifetime of a page. Click on the eye icon in the top to create a new live expression.

Taking high quality screenshots

In DevTools, click the Toggle device toolbar icon (Cmd+Shift+M or Ctrl+Shift+M) to enter the responsive design mode.
In the device toolbar, click More options (⋮) > Add device pixel ratio. In the action bar at the top of the viewport, select a DPR value from the new DPR drop-down menu. Default is 2, but you can bump it upto 3!
Click More options > select Capture screenshot for viewport or Capture full size screenshot for the entire page.

By putting devtools in device mode and then increasing the device pixel ratio, you can take super high quality screenshots.

devtools image

Firefox devtools

Taking screenshots

Open the Console panel, run the command :screenshot --dpr 3 to take a high definition screenshot of the page with the device pixel ratio set to 3.
To capture a full page screenshot, just add --fullpage to the end and --screenshot .header to capture a screenshot of a node that can be identified by a selector.

Console logs

Logging in NodeJS

To see the entire object and not get the annoying [Object object] when console logging in nodejs, use the console.dir(obj, {depth: null}) method.

console.dir(person, { depth: null });
/*
{
    username: 'johndoe',
    meta: {
        firstName: 'John',
        lastName: 'Doe',
        profile: {
            address: { street: '123 Main St', city: 'AnyTown' }
        }
    }
}
*/

Styling logs

Using the %c interpolator at the beginning of a log message will style it accordingly with CSS in the console.

The second argument to console.log() will then be the appropriate CSS styles in a string

console.log("%c some text here", "font-size:2rem;color:blue");

For this reason, I also built this class for logging colors in the browser:

const defaultConsoleStyles = {
  error: "color: red; font-weight: bold;",
  info: "color: blue; font-weight: bold;",
  success: "color: green; font-weight: bold;",
};

export const BasicColorLogger = createColorLogger(defaultConsoleStyles);

export function createColorLogger<T extends Record<string, string>>(
  consoleStyles: T
) {
  const temp: Partial<
    Record<keyof typeof consoleStyles, (message: any) => void>
  > = {};
  for (const [key, value] of Object.entries(consoleStyles)) {
    temp[key as keyof typeof consoleStyles] = (message: any) => {
      console.log(`%c${message}`, value);
    };
  }

  const ColorLogger = temp as Record<
    keyof typeof consoleStyles,
    (message: any) => void
  >;
  return ColorLogger;
}

Log levels

console.warn(string) : displays a message as a warning
console.error() : displays a message as an error
console.info() : displays a message as information
console.clear() : clears the console

console.clear();
console.warn("A warning with console.warn()");
console.error("A message styled like an error with console.error()");
console.info("A message styled as information with console.info()");

Viewing DOM elements

console.dir(element) : console logs the element not just as HTML, but as a DOM element object, allowing you to see all its properties.

Console groups

Console groups organize all log messages inside a group to be inside a collapsible toggle.

console.group(groupname) : begins a logging group with the specified group name.
console.groupEnd() : ends the most recent logging group, closing the toggle.

Using console groups allows you neaten out console messages by grouping them together under a toggle. The way to do this is to position all related log messages inside a group, using this syntax:

console.group("groupname");
// log messages here
console.groupEnd();

console.group("dictionary stuff");
console.log(dogs[0].name);
console.log(dogs[1].name);
console.groupEnd();

Timing

console.time(tag) : starts timing with a specified tag
console.timeEnd(tag) : ends timing with the specified tag, and displays elapsed time to the console.

console.time("saying hello");
console.log("hello");
console.timeEnd("saying hello");

the way to use this is to start time for a specific activity using console.time(), and then end print out the elapsed time using console.timeEnd() when the activity is finished.

`console.table()`

The console.table() method takes in an array of objects all with the same structure and displays them in a table.

Console assertions

Use console.assert() to assert a truthy value and print out an error message if not true

console.assert(condition: boolean, message: any)

Devtools basics

When you right click on an element, here all the different options you have available to you:

copy element : you can copy an element, it's selector, or xpath. You can then paste the element back in the elements panel
hide element: You can choose to visually hide an element or delete it from the page.
scroll into view: You can scroll to the selected element

Symbols

These builtin variables can be used in the devtools console.

$0 : the last selected element. You can continue this pattern with $1 for the 2nd recently selected, and so on. Think of it exactly like a stack. Last in, first out.
$_ : the last returned values
$(selector : string) : JQuery builtin for document.querySelector()
$$(selector : string) : JQuery builtin for document.querySelectorAll()
copy(variable): Copies whatever value of the variable you pass in to the clipboard. Super helpful.

21 tips​

Taking high quality screenshots​

Firefox devtools​

Taking screenshots​

Console logs​

Logging in NodeJS​

Styling logs​

Log levels​

Viewing DOM elements​

Console groups​

Timing​

console.table()​

Console assertions​

Devtools basics​

Mastering the Context menu​

Symbols​