Authenticity and Authority in Leadership

Any team or organization needs strong leadership. A strong leader may encourage and inspire their team members to accomplish great things. But in order to succeed, leaders need to have two crucial…

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Understanding TypeScript

Besides, TypeScript offers all of JavaScript’s features. Because all the TypeScript codes finally are compiled in JavaScript.

In short, TypeScript is a superset of JavaScript. JavaScript is still very important for a typescript developer.

In TypeScript, there are two ways to assign the type to a variable (similar to Dart):

I prefer the first way since it ensures the variable has the type I want and it needs less the codes :)

As JavaScript, TypeScript has the basic types, such as number, string, boolean, bigint, symbol, null, undefined. Besides, TypeScript has more.

unknown: It describes the type of variable that we do not know when we are writing an application.

any: It refers to any type. the variable with any type is the same as the variable in JavaScript.

There is an example to explain the difference between any and unknown . But in practice, I wouldn’t assign b as unknown because I know b is a number.

null and undefined: these two are the same as those in JavaScript. However, when using the --strictNullChecks flag, null and undefined are only assignable to unknown, any and their respective types .

In null and undefined, the string variable can’t be assigned by null . This problem can be solved by union type.

This kind of assignment ensures the variable can not be null if we don’t use union type. It avoids many bugs.

It is a type that represents the non-primitive type, i.e. anything that is not number, string, boolean, bigint, symbol, null, or undefined.

To define the types of the properties, we use {} :

Or, we can use an interface , which will be presented later.

It is very useful when we visit a property of an object. For example:

Function type contains parameters’ type and return’s type

That means a function takes firstName as a required parameter and lastName as an option parameter. Both of them has the string type. And the function return a value with the string type.

If the function returns nothing, we use void .

After ES6, JavaScript has class . The class in JavaScript can

TypeScript class can do these, too. Beside, The class in TypeScript can

Abstract classes are base classes from which other classes may be derived. They may not be instantiated directly.

Unlike an interface, an abstract class may contain implementation details for its members.

Methods within an abstract class that are marked as abstract do not contain an implementation and must be implemented in derived classes.

For example, to create an abstract class:

To extend an abstract class:

TypeScript’s interface is very powerful. It defines the types of properties of an object. It is widely used in real-world project. For example, when the front-end receives a json, it will turn the json into an object. We use interface to define the type of the object’s properties.

In the section “object”, I defined Text type. Now, I use interface to redo it.

Both two methods works. But why do we use interface in real-world project ? Because the interface can do more than that.

Interface can have optional properties. For example, we have a text without id. The interface can be created as followed:

It’s very common when we create a new text. Because id is not existed on server-side when it is just create at front-end.

Interface can have readonly properties. Usually, we don’t want the ID of text changed by the user. The interface can be set:

Interface can add indexable types. When we receive the information like title, author, date, etc. These aren’t presented in Text interface. We can used indexable types.

It adds the flexibility to the interface, but loses the security. It may increase the chance of writing bugs. It’s better to define all the properties.

Interface can be extended by the class. It helps define the attributes’ types and the methods’ types of class.

Interface can be extended by another interface. It’s usually used by generic, which is another powerful tools in TypeScript, presented in the next section.

The components we created should not only have well-defined and consistent APIs, but are also reusable. To make that happen, we need generic.

Generic type can be used in the function. It makes the function reusable.

For example, a function is used by both component A and component B. Component A passes a string to this function, while component B passes a number. Of course, we can use any or the union type string|number as the type of the parameter. But, the better practice is using generic:

Generic keeps both the flexibility and security. It not only makes fn take any kind of the parameter, but also, ensures the parameter passed in the fn has the type we want.

Generic type can be used in the class. It makes the class reusable. It’s widely used in creating the components.

Now, the component A can take anything as its item. But, the function getItemName won’t work because TypeScript doesn’t know item has name property. To fix this, we need to use interface.

The generic extends the Item interface. Now, TypeScript knows item has name .

TypeScript improves the security of the codes. It helps the developers make sure what kind of the variable they use. Meanwhile, TypeScript gives the flexibility to developers, too. For example, the interface and the generic let the codes reusable.

The problem is how to balance the security and flexibility. The bad practice may lose the advantage of TypeScript. For example, if we use any everywhere, we lose the security. If we don’t use any or generic type, the codes will be hard to reuse.

No tutorial can give us the best methods. Practice makes perfect. Just start to use TypeScript, and find you only way.

Authenticity and Authority in Leadership

Understanding TypeScript

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