Angular's next feature @let syntax

We can check the pull request here: https://github.com/angular/angular/pull/55848

Let's discuss the various use cases and advantages of the new @let syntax.

The @let syntax allows us to declare and use local variables within our Angular templates.

@let user = user$ | async;
@let greeting = user ? 'Hello, ' + user.name : 'Loading...';

<h1>{{ greeting }}</h1>

In the above example, user$ is an observable that emits user data. The @let syntax simplifies handling asynchronous data and conditional rendering.

🚀 Use Cases:

➖ Using the async pipe directly in multiple places can lead to multiple subscriptions, which is inefficient and can cause performance issues:

<div>{{ total$ | async }}</div>
<div>{{ total$ | async }}</div>

The solution is to use the @let syntax to declare a variable for the observable value. This approach ensures a single subscription.

@let total = total$ | async;

<div>{{ total }}</div>
<div>{{ total }}</div>

➖ One of the most annoying issues with signals is their lack of type narrowing ability within the template. We can use the @let feature to resolve this problem:

@let txType = tx().type;

@switch(txType) {
  @case('a') {}
  @case('b') {}
}

@let address = person()?.address();

@if (address) {
 <app-address [address]="address">
}

➖ The @let syntax particularly useful within @for loops. We can create intermediate properties directly in the template, enhancing readability and reducing the need for additional component logic:

@for (user of users(); track user.id) {
  @let address = user.address;

  <div>
    <h3>User: {{ user.name }}</h3>
    <div>
      <p>Street: {{ address.street }}</p>
      <p>City: {{ address.city }}</p>
      <p>Zipcode: {{ address.zipcode }}</p>
    </div>
    @for (order of user.orders) {
      <div>
        <h4>Order: {{ order.id }}</h4>
        <p>Product: {{ order.productName }}</p>
        <p>Quantity: {{ order.quantity }}</p>
      </div>
    }
  </div>
}

➖ Using an expensive pipe multiple times in a template often necessitates creating a property in the component to store the transformed data. With the @let syntax, we can declare and reuse a transformed variable once, reducing the computational load and keeping our template clean:

@let someResult = someData | somePipe;

<p>{{ someResult }}</p>
<p>{{ someResult }}</p>

✨ Conclusion

This new feature enhances the development experience for Angular developers by addressing common challenges such as managing falsy values, avoiding multiple subscriptions, and reducing repetitive code.

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I hope you found it helpful. Thanks for reading. 🙏

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