80 lines
2.2 KiB
Markdown
80 lines
2.2 KiB
Markdown
---
|
|
tags: [OOP]
|
|
---
|
|
|
|
# Module pattern
|
|
|
|
> Come back and compare this with learning from Node.js
|
|
|
|
With the module design pattern we create encapsulation: the variables and
|
|
functions (as methods) are kept private inside the module and cannot be
|
|
overwritten. This design pattern is familiar from Node.js development: every
|
|
package you import into your project and download from NPM is a module.
|
|
|
|
Generally you will create the module as a class, import it and then instantiate
|
|
a new instance. However for private development, you could just as well use an
|
|
object and duplicate it with `Object.create`.
|
|
|
|
## Example
|
|
|
|
Here is an example of a simple module that returns the age of a person.
|
|
|
|
```js
|
|
export default class Age {
|
|
constructor(name, birthYear) {
|
|
this.name = name;
|
|
this.birthYear = birthYear;
|
|
}
|
|
currentYear() {
|
|
return new Date().getFullYear();
|
|
}
|
|
get age() {
|
|
return this.currentYear() - this.birthYear;
|
|
}
|
|
}
|
|
```
|
|
|
|
```js
|
|
const martha = new Age("Martha", 1997);
|
|
console.log(martha.age); // 24
|
|
```
|
|
|
|
## Controlling access
|
|
|
|
In the example above, `aValue` could be edited in instantiations of the class.
|
|
Given that modules should not be overwrittable, you could make it a private
|
|
property on the class. The benefit of getters and setters is that they dictate
|
|
what can be modified and retrieved from the module. So if you use `get` and
|
|
`set` you can prevent overwrites.
|
|
|
|
## Object modules
|
|
|
|
If you want to use an object instead of a class, you have to take greater care
|
|
to ensure that the objects are not overwritable. **Also you cannot use the `#`
|
|
modifier to make properties private.**
|
|
|
|
- Use getters and setters for updating and retrieving values
|
|
- Use `Object.seal` to prevent changes to the parent object
|
|
- Instead of using getters and setters, for individual properties you can set
|
|
`writable` to be `false` for properties that you don't want changed
|
|
|
|
There are examples of each in the following:
|
|
|
|
```jsx
|
|
export const age = {
|
|
name: "",
|
|
birthYear: new Number(),
|
|
currentYear() {
|
|
return new Date().getFullYear();
|
|
},
|
|
get age() {
|
|
return this.currentYear() - this.birthYear;
|
|
},
|
|
};
|
|
|
|
Object.seal(age);
|
|
Object.defineProperty(age, "aValue", {
|
|
value: 6,
|
|
writable: false,
|
|
});
|
|
```
|