js file minify fail on Harmony(ES6+) option checked

[jeffy-g]

Koala version

v2.2.0

Bug report or feature request?

Bug report

summary:

js file minify fail on Harmony(ES6+) option checked. (uglify-js@3.0.4

tsc: compile with target "es6"

ts file

declare interface IDummy {
    file(): void;
}

namespace lengthbug {
    export function createMessageFileX(): IDummy {
        return new MessageFileX();
    }
    /*export*/ class MessageFileX implements IDummy {
        private _messages: Array<JQuery> = [];
        public constructor() {}
        public file(): void {
            if (this._messages.length > 10) {
                console.log("out of bound!");
            }
        }
    }
}

js file

var lengthbug;
(function (lengthbug) {
    function createMessageFileX() {
        return new MessageFileX();
    }
    lengthbug.createMessageFileX = createMessageFileX;
    class MessageFileX {
        constructor() {
            this._messages = [];
        }
        file() {
            if (this._messages.length > 10) {
                              //^^^^^
                console.log("out of bound!");
            }
        }
    }
})(lengthbug || (lengthbug = {}));

error message appeared.
that message is:

"Cannot read property 'length' of undefined"
...

this is sample source.
well, these are uglify-js bug...

however, this is no error.

var lengthbug;
(function (lengthbug) {
    function createMessageFileX() {
        return new MessageFileX();
    }
    lengthbug.createMessageFileX = createMessageFileX;
    class MessageFileX {
        constructor() {
            this._messages = [];
        }
        file() {
            if (this._messages.length > 10) {
                console.log("out of bound!");
            }
        }
    }
    lengthbug.MessageFileX = MessageFileX; // <-- 
})(lengthbug || (lengthbug = {}));

[zaygraveyard]

This is a bug in UglifyJS, see mishoo/UglifyJS#2028
Also while test this I found another bug mishoo/UglifyJS#2027

[zaygraveyard]

I will improve the error message so it more descriptive.

[jeffy-g]

i hope your improvement :-)

thanks 👍

[zaygraveyard]

Improve the error message so it more descriptive in v2.3.0