[英]What is the use case for declaration merging?
I'm reading a bit about declaration merging in TypeScript and I have a hard time grokking the use case for it, specifically for interfaces. 我在阅读有关TypeScript中声明合并的内容 ,并且很难理解它的用例,尤其是对于接口。
In their documentation, they have this example: 在他们的文档中,他们有以下示例:
That is, in the example:
也就是说,在示例中:
interface Cloner { clone(animal: Animal): Animal; } interface Cloner { clone(animal: Sheep): Sheep; } interface Cloner { clone(animal: Dog): Dog; clone(animal: Cat): Cat; }
The three interfaces will merge to create a single declaration as so:
这三个接口将合并以创建单个声明,如下所示:
interface Cloner { clone(animal: Dog): Dog; clone(animal: Cat): Cat; clone(animal: Sheep): Sheep; clone(animal: Animal): Animal; }
Why would one want to create three separate interfaces instead of the resulting declaration? 为什么要创建三个单独的接口而不是结果声明?
For example, you might want to add a method to the window object, so you'll do this: 例如,您可能想向window对象添加一个方法,因此您可以这样做:
interface Window {
myMethod(): string;
}
window.myMethod = function() {
...
}
This is very useful when you need to polyfill: 当您需要填充时,这非常有用:
interface String {
trimLeft(): string;
trimRight(): string;
}
if (!String.prototype.trimLeft) {
String.prototype.trimLeft = function() { ... }
}
if (!String.prototype.trimRight) {
String.prototype.trimRight = function() { ... }
}
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