Angular - tips and tricks

Recently, I completed a project in Angular and along the way, there were some things I learned that might provide some useful direction for other developers. So, if you’re diving into Angular for the first time or just looking for a better way to manage your Angular projects, here are some tips and tricks you might want to keep in mind along the way.

Unsubscribe from RxJS observables

Every time a component or directive is destroyed, the subscription to observable remains active. So it is important to unsubscribe from it to release the memory in the system, otherwise, you will have a memory leak. There are many approaches but I prefer to use takeUntil function:

import { Component, OnDestroy, OnInit } from "@angular/core";
import { Observable, Subject, interval } from "rxjs";
import { takeUntil } from "rxjs/operators";

@Component({
    selector: "app-test",
    template: `<div>Test</div>`
})
export class TestComponent implements OnDestroy, OnInit {
    private destroyed$ = new Subject<void>();

    private ticks$ = interval(1000);

    public ngOnInit() {
        this.ticks$
            .pipe(takeUntil(this.destroyed$))
            .subscribe(data => console.log(data));
    }

    public ngOnDestroy() {
        this.destroyed$.next();
        this.destroyed$.complete();
    }
}

You can read more about takeUntil functions here : http://reactivex.io/documentation/operators/takeuntil.html

If you like decorators you can take a look at this package that provides a declarative way to unsubscribe from observables when the component destroyed : https://github.com/NetanelBasal/ngx-take-until-destroy

PS: You don’t need to worry about unsubscribing if you are using AsyncPipe because it unsubscribes automatically. Also, methods than take(n), takeWhile(predicate), first() and first(predicate) unsubscribes by their-self.

Create sexier imports with typescript aliases

When codebase starts to grow you will see imports such as the following:

import {MyComponent} from '../../../../../../shared/components/mycomponent'

This is very annoying because you don’t know how many dot-dot-slashes you need to write in order to go to the right place. Actually, Typescript compiler allows to use path mapping so we can import our files like this :

import {MyComponent} from '@shared/components/mycomponent'

All we need to do is to define the paths and baseUrl properties in the compilerOptions section in the tsconfig.json file. It’s important to know that all paths are resolved relative to baseUrl.

Example :

{
    "compilerOptions": {
    ...
    "baseUrl": "./src",
        "paths": {
            "@shared/*":["app/modules/shared/*"],
            "@core/*":["app/modules/core/*"]
        }
    ...
    }
}

Use trackBy in *ngFor

When we use *ngFor directive, DOM changes are tracked by object identity. This is fine for most situations, but with the introduction of immutable practices and Redux, we have every time new objects. This means that every time *ngFor will render the list in DOM, but we know that DOM operations are expensive. When we use trackBy with *ngFor, it starts change propagation tracked by given identity and not by object identity.

Example:

<div *ngFor="let post of posts;trackBy:trackByFn"></div>
...
identify(index,item){
    return item.id;
}

More information about trackBy you can find here: https://netbasal.com/angular-2-improve-performance-with-trackby-cc147b5104e5

Use interfaces instead classes

Sometimes we need some models or definitions for the server data. The interfaces can be used for this purpose without additional overhead for the final output. Unlike classes, interfaces are completely removed during build creation and so they will not add any unnecessary code to our final bundle.

Clear all your console.logs in production

During the development we write a lot of console.logs in order to debug our app and sometimes we display some informations that we don’t want our users to see it. We can remove it very simple using few lines of code for production build.

Add this in main.js:

import {environment} from './environments/environment'

if (environment.production) {
  // Remove console logs in production
  window.console.log = () => {}
  enableProdMode()
}

Inspect your bundle with webpack-bundle-analyzer

Analyzing bundle it’s a good start to improve app performance. Visualizing webpack output helps you to understand the composition of your bundle, to see what modules take space in it and to identify unnecessary dependencies.

More information about this tool you can read here: https://alligator.io/angular/bundle-size/

Don’t Lazy-Load the Default Route

Lazy loading modules it’s a good feature that helps us decrease the startup time and load pieces of code on demand. We don’t need to load everything at startup, we only needs to load what user expects to see when app loads. A bad practice is to lazy-load the default route.

Let’s suppose that we have the following configuration:

const routes: Routes = [
  {path: '', redirectTo: '/mymodule', pathMatch: 'full'},
  {path: 'mymodule', loadChildren: './mymodule.module#MyModule'},
]

When the user opens the application, he will be redirected to /mymodule route which will trigger the lazy-loading of MyModule. This will trigger an extra HTTP call to download mymodule.module and will perform some unnecessary operations ( parsing and evaluation of JavaScript VM). In result, this slows down the initial page rendering. So it’s a good practice to declare the default page route as non-lazy.

Catch all errors with a custom error handler

Angular provides a built-in global exception handling service so when an error occurs, this service will catch it and will print the error details in the console. We can extend this exception handler to add some additional functionalities like to send the errors to your backend server for analytics or other reasons.

Extending Angular’s Error Handler

Extending Angular’s Error Handler it’s a easy task. All we need to do is to create a class that extends Angular’s ErrorHandler and override the handleError method.

Example:

import {ErrorHandler} from '@angular/core';

export class AppErrorHandler extends ErrorHandler {
    constructor(){
        super(false);
    }

    public handleError(error: any): void {
        // Add your logic here.
        super.handleError(error);
    }
}

After that, we should register our custom AppErrorHandler in app.module.ts:

@NgModule({
    declarations: [ AppComponent ],
    imports: [ BrowserModule ],
    bootstrap: [ AppComponent ],
    providers: [
        {provide: ErrorHandler, useClass: AppErrorHandler}
    ]
})

More information you can find here: https://www.loggly.com/blog/angular-exception-logging-made-simple/

Bonus:

Wrap your console.log arguments in an object literal to print the variable name along with its value.

console.log(isLoggedIn)
console.log({isLoggedIn})

Thanks for reading this article, I hope that you enjoyed it!