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I have this code

function changeFunc() {
    return function(target: any, title: string, descriptor: PropertyDescriptor) {

        descriptor.value = function () {
            console.log(this.name);
        };

        return descriptor;

    }
}


class Man {
    name: string = "asdsds";

    constructor(name: string) {
        this.name = name;
    }

    @changeFunc()
    getName() {
        console.log("Hello");
    }

}


var man = new Man('Manos Serifios');
man.getName();  

In other words i try (with the decorator) to change the method

getName() {  
    console.log("Hello");  
}  

with this

function () {
    console.log(this.name);
}

but this.name evaluated as undefined.

If i console log the "this" it seems that is the right(instance man).

I have this code

function changeFunc() {
    return function(target: any, title: string, descriptor: PropertyDescriptor) {

        descriptor.value = function () {
            console.log(this.name);
        };

        return descriptor;

    }
}


class Man {
    name: string = "asdsds";

    constructor(name: string) {
        this.name = name;
    }

    @changeFunc()
    getName() {
        console.log("Hello");
    }

}


var man = new Man('Manos Serifios');
man.getName();  

In other words i try (with the decorator) to change the method

getName() {  
    console.log("Hello");  
}  

with this

function () {
    console.log(this.name);
}

but this.name evaluated as undefined.

If i console log the "this" it seems that is the right(instance man).

• javascript
• typescript

Share Improve this question Follow asked Jan 11, 2018 at 22:57 Manos SerifiosManos Serifios 57722 gold badges88 silver badges2222 bronze badges 2

• maybe descriptor.value = function () { console.log(target.name); };. I am just guessing and have no experience with typescript decorators – 2pha Commented Jan 12, 2018 at 0:30
• @2pha no, i tried it – Manos Serifios Commented Jan 12, 2018 at 9:44

Add a ment  | 

3 Answers 3

Sorted by: Reset to default 7

You don't have the context of a specific object instance inside the decorator method. The parameters are the following (from https://www.typescriptlang/docs/handbook/decorators.html):

Either the constructor function of the class for a static member, or the prototype of the class for an instance member.

The name of the member.

The Property Descriptor for the member.

You can do a little Hack. Replace your code

descriptor.value = function () {
  console.log(this.name);
};

with this nice trick:

descriptor.value = function () {
  // Hack 
  const self = this as Man;
  console.log(self.name);
};

@hackerman's answer worked for me, as it seems to just be a typing issue. An alternative solution would be to actively define the type of this for that function:

descriptor.value = function (this: Man) {
  console.log(this.name);
};

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