如何在打字稿中定義帶有“this”上下文的函數

Question

type Animal = {
    name: string
}

function getBear(this: Animal) : Animal {
    this.name = "hi"
    return this
}

console.log(getBear().name)

任何人都可以幫我解決這個問題，我無法調用 getBear 函數

Answer 1

您不能這樣做，因為getBear的this上下文在您調用它時未綁定到Animal 。 簡單地告訴 TypeScript this是一個Animal是不夠的，您還必須使用該上下文調用您的函數。

在這種情況下，您需要像這樣調用它。

type Animal = {
    name: string
}

function getBear(this: Animal) : Animal {
    this.name = "hi"
    return this
}

console.log(getBear.call({ name: "test" }).name)

Answer 2

您可以通過 3 種方式調用它：

type Animal = {
    name: string
}

function getBear(this: Animal, a: string): Animal {
    this.name = a
    return this
}

// First one 

// function.call(objcontext,parameters) calls a function under a different object context.
// read more at : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call

console.log(getBear.call({ name: "test" }, "Username").name)

// Here we create a object 
//second
console.log(new (getBear as any)("Username").name)

//third
console.log(new (<any>getBear)("Praveen").name)