DevTools
Tools & tricks
⚙️
Hello!
Im Jon Rojí
Frontend at Sngular
🦄 🖌️ 🍺
Disclaimer!
DETECT, TOOLS AND TIPS, NOT FIX
✏️ DOM & styles
▶️ Console Master
📂 Sources
✋ Debuggers & Breakpoints
🌐 Network
📈 Coverage
🧙♀️ Tools & tricks
Elements
store the element as temp1 ... temp
copy css/xpath selectors
QA
element state modifier
element state modifier
classes toggle
element state modifier
classes toggle
class adition
hold to change the file
Deactivate Ancestors check in order to avoid info overflow
Event listeners of the element
Accessibility
Check the role attribute in order to check what people expects from the element
cmd + shift + P
Console
$0 - References the selected HTML element
Execution context from the debugger
Live expressions!
JS statements that executes every 250ms
console.log({ myProp });
console.assert(NaN == NaN)
console.table([{a:1, b:2}, {a:2, b:3}]);
console.log("%cStop", "color:red;font-family:system-ui;font-size:4rem;-webkit-text-stroke: 1px black;font-weight:bold" );
Sources
One of the most important and complex areas on DevTools
Show loaded files
Allow us to set breakpoints (not only on js)
Allow us to override entire files!
Blackbox scripts!
Sources
Use search tool
Show scope of the detected source
Page
Filesystem
We can link the served content with our files,
and save the edited content!
❤️ Great editing styles
Look for the green point
❤️ Awesome for local development
Overrides
We can replace a served file
with a custom and editable file!
- active Enable Local Overrides
- Select the file on network and save for override
❤️ Great for testing new solutions
Look for the purple point
❤️ Awesome for "before push" testing
Overrides
We can replace a served file
with a custom and editable file!
- active Enable Local Overrides
- Select the file on network and save for override
❤️ Great for testing new solutions
Look for the purple point
❤️ Awesome for "before push" testing
Threads & Watch
Threads
Useful working with web workers
Can pause both threads at the same time
Threads & Watch
Threads
Useful working with web workers
Can pause both threads at the same time
Watch
Show info about variables values
Breakpoints!
JS breakpoint
Stop JS execution on the selected line or debugger
Breakpoints!
Pause
Next statement
Jump into/out of function
Next statement (including functions)
Breakpoints!
Call Stack
Show us all the functions called from the breakpoint
Blackbox the libraries
and frameworks!
Scope
Show us the local and global context in the moment of the execution pause so we dont need to hover all props on the source file
Console context becomes the local!
Breakpoints!
XHR Breakpoints
Type a url fragment to stop on xhr request
The Call Stack will show where the request is initiated, allowing us to navigate there
Breakpoints!
DOM elements Breakpoints
Select a HTML Element and select Break on
The Call Stack will show where the modification is requested, useful using events or toggling attributes
Breakpoints!
Event Listener Breakpoints
You can activate breakpoints for any kind of event, in order to analize where the application is listening for
You can see the Global listeners setted too
Network
One of the best tools on DevTools
Allow us to limit the connection speed
Test like a 3g network or Offline (nice for PWA)
Great for look into the waterfall graph
Block requests by URL or Domain
Allow us to check the web behaviour without the blocked resource
Save for overrides
Magic
More tools > Coverage
(cmd + shift + p)
Check unused CSS & JS
Performance
The worse config, the better
The redpoints shows bottlenecks or fps problems
Shows CPU use. Discover critical points
Screenshots will help identifying the critical points
Performance is the art of doing less
Scripting and Rendering
426.2 ms + 279.0 ms
Check colors for info!
requestIdleCallback
requestAnimationFrame
scripting main enemy
blocking the thread
Select a problematic stack call, and analyze
Navigate on stack call to detect problematic points
More tools > Rendering
(cmd + shift + p)
FPS meter 🧭
Paint flashing 🖼️
Scrolling performance issues 🧶
On CI!
lighthouse-ci
More tools > Performance monitor
(cmd + shift + p)
@jnroji