https://github.com/jdegand/bug-cd
Angular Challenges #32 Bug Change Detection
https://github.com/jdegand/bug-cd
angular angular-challenges change-detection
Last synced: 4 months ago
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Angular Challenges #32 Bug Change Detection
- Host: GitHub
- URL: https://github.com/jdegand/bug-cd
- Owner: jdegand
- Created: 2023-09-21T23:22:55.000Z (almost 2 years ago)
- Default Branch: main
- Last Pushed: 2023-10-04T18:15:45.000Z (almost 2 years ago)
- Last Synced: 2025-01-22T09:13:37.524Z (5 months ago)
- Topics: angular, angular-challenges, change-detection
- Language: TypeScript
- Homepage:
- Size: 114 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Bug Cd
[Angular Challenges](https://github.com/tomalaforge/angular-challenges) #32 Bug Change Detection Solution
## Built With
- [Angular](https://angular.io)
- [Angular CLI](https://github.com/angular/angular-cli) version 16.2.2.
## Directions
In this small application, we have a navigation menu to route our application to either `barComponent` or `FooComponent`. However our application is not loading and no errors are displayed inside the console.
### Statement
The goal of the challenge is to debug this application and make it work.
#### Hints
Hint 1
If you comment out `routerLinkActive="isSelected"` inside `NavigationComponent`: the application loads correctly.
Hint 2
If you open the [`RouterLinkActive` source code](https://github.com/angular/angular/blob/main/packages/router/src/directives/router_link_active.ts) and go to **line 196**, Angular is calling `this.cdr.markForCheck` inside a microTask which triggers a new CD cycle. If you comment out this line, the application loads again, however the bug is not inside the Angular Framework.
## Thoughts
- App is slow and you can't refresh it.
- I didn't like the order of the routes so I changed them. Although it doesn't really matter in this case, I always prefer to have empty routes at the bottom (with a wildcard route as the final route).
- Having getMenu function calls inside the template is a problem.
- Use a pipe ? ngOnChanges ?
- I initially leaned towards ngOnChanges as many challenges I have already used pipes.
- The fake backend response (string) actually makes this harder to fix with ngOnChanges.
- There will be typing issues if you just pass a string to menus. Once you fix that, then you call the getMenu function inside of ngOnChanges. Then you have to worry about return types and issues in the template.
- I think it would be preferrable to have the @Input just be the object itself. But that wouldn't be enough as you would need to pass the Input value to a function that adds the prop value inside the ngOnChanges function.
- Ultimately, I think ngOnChanges would require too much modification to the existing code to be a realistic solution.
- I found some great articles and there is an easy fix. Use a memo function and you can keep the function calls in the template. See [this article](https://itnext.io/its-ok-to-use-function-calls-in-angular-templates-ffdd12b0789e) for the memo function and explanation.
## Useful Resources
- [Angular Docs](https://angular.io/api/router/RouterLinkActive#description) - RouterLinkActive
- [Stack Overflow](https://stackoverflow.com/questions/33520043/how-to-detect-a-route-change-in-angular) - how to detect a route change in angular
- [Stack Overflow](https://stackoverflow.com/questions/57916707/angular-8-ui-observable-not-triggering-change-detection-changedetectionstrateg) - angular 8 observable not triggering change detection
- [Stack Overflow](https://stackoverflow.com/questions/41364386/whats-the-difference-between-markforcheck-and-detectchanges) - whats the difference between markForCheck and detectChanges ?
- [Medium](https://medium.com/@andre.schouten_ff/whats-the-difference-between-markforcheck-and-detectchanges-in-angular-fff4e5f54d34) - difference between markForCheck and detectChanges
- [Medium](https://medium.com/showpad-engineering/why-you-should-never-use-function-calls-in-angular-template-expressions-e1a50f9c0496#:~:text=In%20this%20article%2C%20we%20learned,calls%20in%20Angular%20template%20expressions.) - why you should never use function calls in angular template expressions
- [Blog](https://itnext.io/its-ok-to-use-function-calls-in-angular-templates-ffdd12b0789e) - its ok to use function calls in angular templates
- [Dev.to](https://dev.to/nickraphael/ngonchanges-best-practice-always-use-simplechanges-always-1feg) - ngOnChanges best practice always use simpleChanges