Go to definition cannot work as expected

[davisduan]

Here is the case:

var x = {
    "abc": function () {
        return 1;
    },
    "def": function () {
        this.abc(); //cannot go to definition
    }
};

This function works well in sublime

[mhegazy]

The issue is not go-to-def. the issue is that the type of this is any in an object literal by default. the rational here is object literals are passed around as property bags, and can be accessed with different this arguments.

If you are running with TS 2.3 or later, we have a change only under --noImplicitThis that allows for a stricter type of this in object literals among other things. go to def should work as expected under this flag.

[davisduan]

@mhegazy Thanks for your explanation. It works after I added the parameter. But I meet the same problem when I put the object as parameter:

Parent.extend("Child", {
    "abc": function () {
        return 1;
    },
    "def": function () {
        this.abc(); //cannot go to definition - the type of this is any
    }
});

[mhegazy]

how is Parent.extend defined?

[davisduan]

I don't think it's quite related to the function definition. But you can take jQuery extend function as reference.

jQuery.extend({
    "abc": function () {
        return 1;
    },
    "def": function () {
        this.abc(); //cannot go to definition - the type of this is any
    }
});

[mhegazy]

JQuery.extend is defined with target : any; this pushes a contextual type of any for the function, and thus the this parameter.

if it was defined using generics instead:

declare function extend<T>(target: T): any;

you would get your this type correctly under --noImplicitThis.

You can take this one step further and make the type of this the combination of all the object literal properties using ThisType<T>, so:

declare function extend<T, U, V>(target: T & ThisType<T & U & V>, object1: U & ThisType<T & U & V>, object2: V & ThisType<T & U & V>): any;

extend({
        "abc": function () {
            return 1;
        },
        "def": function () {
            this.abc(); // OK
        }
    },
    {
        "another": function () {
            this.def(); // OK
         }
    },
    {
        "yetAnother": function () {
            this.another(); // OK
         }
    });

you can find more info about the use of ThisType in #14141

[davisduan]

Actually, I just want to use Visual Studio Code to develop in JavaScript, which is is using TypeScript as JS compiler. But I cannot use "declare function ..." in JS code.
Seems it too complex for me to achieve the "Go to definition" function works like sublime.
Anyway, thank you very much. @mhegazy

[mhegazy]

Where is extends comming from? VSCode gets your declarations form an @types package, so updating it should do the trick without you having to change your code.

[davisduan]

Extends is one of functions in my JS library. Here is only a example. I don't think I can add all the functions declaration manually.

[mhegazy]

This issue seems to have been already addressed or is unactionable at the moment. I am auto-closing it for now.