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Here this blog post will be considered as a quick note as I reading through the TypeScript Handbook.

This post will contain some easy-take mistakes and misconceptions about Typescript.

Basic Conceptions & Mechanisms

Interface and Type-alias

We all know in Typescript we could declare our own type structures by using Type-Alias or Interface.

The doc recommend us using Interface and only use Type-alias when we need some certain specified features provide by Type-alias.

The reason mentions is that interface usually has more detailed and well-formed error message compared to type alias.

Structure-focused & Duck types

Typescript actually focus and cares about the structure of the objects. that means it's possible that different types actually depict the same thing and work as the same.

type Point1 = { x: number, y: number };
type Point2 = { x: number, y: number };

interface Point3 {
  x: number,
  y: number
};

function printPoint(pointInfo: Point1) {
  console.log(`<Point x=${pointInfo.x} y=${pointInfo.y}>`);
}

printPoint(pointinfo as Point2); // correct
printPoint(pointInfo as Point3); // also correct

As the example above, Point1, Point2 and Point3 actually refer to the same structure and they could substitute each others.

This usually be called the Duck Type system.

Down-leveling

Typescript has the ability to general a lower version ECMAScript code (which could improve compatibility of your TypeScript project). You can even target the js output to ES3 standard.

Notice that most of major browser currently support ES5 standard, so in most cases you can feel free to target to ES5 version.

StrictMode

The most important ones are:

• noImplicitAny: Do NOT allow type infers result in any. Which means all type should be properly marked / inferred.
• strictNullChecks As the names suggests, enabling this will require us to deal with null and undefined explicitly in our code.

Also there exists a over-all param called strict. You could add it to the command when using CLI, or add "strict": true to your tsconfig.json. This will turn on all strict check feature in default, but you have the right to opt-out some of them individually.