type Animal = {
    name: string
}

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

console.log(getBear().name)

Could any one help me with this , i am not able to call the getBear function

type Animal = {
    name: string
}

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

console.log(getBear().name)

Could any one help me with this , i am not able to call the getBear function

• javascript
• typescript
• typescript-typings

Share Improve this question Follow asked Nov 4, 2021 at 7:13 PDHidePDHide 20k22 gold badges4242 silver badges5656 bronze badges 1

• 1 You explicitly define that this has to be Animal, but you call getBear on no object so it is void. – t.niese Commented Nov 4, 2021 at 7:19

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2 Answers 2

Sorted by: Reset to default 6

You can't do this because the this context of getBear is not bound to an Animal when you call it. Simply telling TypeScript that this is an Animal isn't enough, you also have to call your function with that context.

In this case you would need to call it like this.

type Animal = {
    name: string
}

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

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

You can call this 3 ways:

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/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)