Prototype assignment should take the type of the initializer and not require a literal

[minestarks]

This is a feature request based on actual VS customer code.

TypeScript Version: 3.9.2

Search Terms: ES5 class javascript prototype assignment constructor function

Expected behavior: In the example below, the prototype for test.class should include properties from testPrototype.

Actual behavior: Per @sandersn this pattern is recognized in the binder and only uses syntactic information, therefore does not use the type information from testPrototype .

Related Issues: #39167 from same user code. Also #33454 maybe?

Code

var test = {};
test.testPrototype = {
    add: function (i) {
    }
}

test.class = function (name) {

    function getName() {
        return name;
    }

    this.name = getName();
}

test.class.prototype = test.testPrototype; 

var t = new test.class("test");
t.name
t.add // EXPECTED: Binds to `add` from the prototype, ACTUAL: doesn't


//
// Same pattern works when a literal is assigned to the prototype:
//

var test2 = {};

test2.class = function (name) {

    function getName() {
        return name;
    }

    this.name = getName();
}

// replaced `test.testPrototype` with a literal 
test2.class.prototype = {
    add: function (i) {
    }
}; 

var t2 = new test2.class("test");
t2.name
t2.add // ACTUAL: `add` bound correctly

Compiler Options

{
  "compilerOptions": {
    "noImplicitAny": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "alwaysStrict": true,
    "esModuleInterop": true,
    "checkJs": true,
    "allowJs": true,
    "declaration": true,
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "moduleResolution": 2,
    "target": "ES2017",
    "jsx": "React",
    "module": "ESNext"
  }
}

Playground Link: Provided