TypeError: b is undefined in __extends

[drake7707]

class B extends A {
    constructor(msg:string) { 
        super(msg);
    }
}

class A {
    constructor(public msg:string) {

    }
}

If the super class of B is defined after A you'll get a runtime error.

Just tested the above code in the typescript playground and I get the same error

[mhegazy]

This issue has been discussed in #21 and has been closed for some bigger issue. this has been a reoccurring pain though.

The consensuses in #21 is to show a compiler error about what the wrong order. we should be able to do this easily using checker.ts::isDefinedBefore.

[nbellowe]

Why isn't this expected behavior?

class B extends A {
    constructor(msg:string) { 
        super(msg);
    }
}
class A {
    constructor(public msg:string) {

    }
}

Generates

var __extends = ... we've all seen this! :) 
var B = (function (_super) {
    __extends(B, _super);
    function B(msg) {
        _super.call(this, msg);
    }
    return B;
})(A);
var A = (function () {
    function A(msg) {
        this.msg = msg;
    }
    return A;
})();

The IIFE after var B = has a parameter of A, but var A = ...isn't called until just after that.

I don't know how you could get the above functionality ... maybe:

var B;
var A;
(function(){
    function b(_super) {
        __extends(B, _super);
        function B(msg) {
            _super.call(this, msg);
        }
        return B;
    }
    function a(){ ... }
    B = b(a);
    A = a;
})()

[DanielRosenwasser]

It's expected, it's just that the compiler should warn you that this will happen.

[danquirk]

As mentioned, dupe of #2854

[mhegazy]

@sheetalkamat has a fix for the class issue since it has been biting users quite frequently.