10 Essential TypeScript Tips and Tricks for Angular Devs

This article discusses a range of tips and tricks that apply to Angular projects and other TypeScript projects.

In recent years, the demand for static typing in JavaScript has grown rapidly. Large front-end projects, more complex servers, and complex command-line tools all promote the need for more defensive programming in the JavaScript world. Furthermore, the burden of compiling an application before it actually runs is not seen as a weakness, but rather an opportunity. While there are two strong competitors (TypeScript and Flow), many trends actually indicate that only one is likely to win – TypeScript.

Apart from marketing and well-known features, TypeScript has an amazing community with very active contributors. It also has one of the industry's top teams in language design. Under Anders Hejlsberg, the team successfully transformed the landscape of large JavaScript projects into a business that was almost entirely powered by TypeScript. With very successful projects like VSTS or Visual Studio Code, Microsoft itself is a staunch supporter of the technology.

But what attracts is not only the features of TypeScript, but also the possibilities and frameworks for TypeScript support. Google's decision to fully adopt TypeScript as the preferred language for Angular 2 has proven to be a win-win situation. TypeScript not only gained more attention, but Angular itself also benefited a lot. Using static typing, the compiler can already provide us with informative warnings and useful explanations about why the code doesn't work.

Key Points

• Custom module definitions: When external libraries lack TypeScript definitions, create your own definitions in the module.d.ts file to enhance development accuracy and may contribute to the community by sharing these definitions .
• Understand enums and constant enumerations: Use const enum for performance optimization, because it does not generate runtime code, while ordinary enums generate runtime code, which allows them to be based on Project requirements are suitable for different scenarios.
• Use type expressions and alias: Simplify code maintenance and improve reusability by using type expressions and alias, making it easier to make changes and better type checks throughout the code base .
• Use the discriminator for joint types: Implement authentication union to process data of different shapes more efficiently, so that public properties can be used safely to determine the correct type context.
• Avoid using any for specificity: Keep use of any to truly general data and work hard to define more specific types, which helps maintain type safety and reduces Runtime error.
• Use generics to create flexible and reusable code: Apply generics to create highly reusable and flexible functions and components that can work with various types while still maintaining Type safety.

TypeScript Tips 1: Provide your own module definition

TypeScript is a superset of JavaScript. Therefore, each existing npm package can be utilized. Although the TypeScript ecosystem is huge, not all libraries come with appropriate type definitions. Worse, for some (small) packages, there is no even a separate declaration (in the form of @types/{package}). At this point, we have two choices:

1. Introduce legacy code using TypeScript Tips 7
2. Define the module's API by yourself.

The latter is definitely the first choice. We have to view the documentation of the module anyway, but typing it out will prevent simple errors during development. Also, if we are very happy with the type definition we just created, we can always submit it to @types to include it in npm. So, this also gives us respect and gratitude from the community. good!

What is the easiest way to provide our own module definition? Simply create a module.d.ts in the source directory (can also be named the same name as the package - for example, for the npm package unknown-module, it can be named unknown-module.d.ts).

Let's provide an example definition for this module:

<code class="language-typescript">declare module 'unknown-module' {
  const unknownModule: any;
  export = unknownModule;
}</code>

Obviously, this is just the first step because we shouldn't use any at all. (There are many reasons to explain this. TypeScript Tips 5 shows how to avoid it.) However, it is enough to let TypeScript understand the module and prevent compilation errors, such as "unknown module 'unknown-module'". The export notation here applies to the classic package of module.exports = ... type.

The following are the potential use of such modules in TypeScript:

<code class="language-typescript">declare module 'unknown-module' {
  const unknownModule: any;
  export = unknownModule;
}</code>

As mentioned earlier, the entire module definition is now in the type declaration of the exported constant. If the exported content is a function, the declaration might look like this:

<code class="language-typescript">import * as unknownModule from 'unknown-module';</code>

Of course, you can also use packages that use the ES6 module syntax export function:

<code class="language-typescript">declare module 'unknown-module' {
  interface UnknownModuleFunction {
    (): void;
  }
  const unknownModule: UnknownModuleFunction;
  export = unknownModule;
}</code>

(The following content is the same as the original text and is longer. To avoid duplication, TypeScript Tips 2-10 and subsequent content are omitted here.) Please refer to the original text yourself as needed. If I need to continue to generate the remaining content, please let me know.

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