[ES6] bug: TypeError: Assignment to constant variable

[Cweili]

Bug report or feature request?

Bug

ES5 or ES6+ input?

ES6+

Uglify version (uglifyjs -V)

3.3.9

JavaScript input

/******/ (function(modules) { // webpackBootstrap
/******/ 	// The module cache
/******/ 	var installedModules = {};
/******/
/******/ 	// The require function
/******/ 	function __webpack_require__(moduleId) {
/******/
/******/ 		// Check if module is in cache
/******/ 		if(installedModules[moduleId]) {
/******/ 			return installedModules[moduleId].exports;
/******/ 		}
/******/ 		// Create a new module (and put it into the cache)
/******/ 		var module = installedModules[moduleId] = {
/******/ 			i: moduleId,
/******/ 			l: false,
/******/ 			exports: {}
/******/ 		};
/******/
/******/ 		// Execute the module function
/******/ 		modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);
/******/
/******/ 		// Flag the module as loaded
/******/ 		module.l = true;
/******/
/******/ 		// Return the exports of the module
/******/ 		return module.exports;
/******/ 	}
/******/
/******/
/******/ 	// expose the modules object (__webpack_modules__)
/******/ 	__webpack_require__.m = modules;
/******/
/******/ 	// expose the module cache
/******/ 	__webpack_require__.c = installedModules;
/******/
/******/ 	// define getter function for harmony exports
/******/ 	__webpack_require__.d = function(exports, name, getter) {
/******/ 		if(!__webpack_require__.o(exports, name)) {
/******/ 			Object.defineProperty(exports, name, {
/******/ 				configurable: false,
/******/ 				enumerable: true,
/******/ 				get: getter
/******/ 			});
/******/ 		}
/******/ 	};
/******/
/******/ 	// getDefaultExport function for compatibility with non-harmony modules
/******/ 	__webpack_require__.n = function(module) {
/******/ 		var getter = module && module.__esModule ?
/******/ 			function getDefault() { return module['default']; } :
/******/ 			function getModuleExports() { return module; };
/******/ 		__webpack_require__.d(getter, 'a', getter);
/******/ 		return getter;
/******/ 	};
/******/
/******/ 	// Object.prototype.hasOwnProperty.call
/******/ 	__webpack_require__.o = function(object, property) { return Object.prototype.hasOwnProperty.call(object, property); };
/******/
/******/ 	// __webpack_public_path__
/******/ 	__webpack_require__.p = "";
/******/
/******/ 	// Load entry module and return exports
/******/ 	return __webpack_require__(__webpack_require__.s = 0);
/******/ })
/************************************************************************/
/******/ ([
/* 0 */
/***/ (function(module, exports, __webpack_require__) {

"use strict";


Object.defineProperty(exports, "__esModule", {
  value: true
});
function foo(a) {
  return console.log(a);
}

exports.default = async function bar(arg) {
  try {
    const a = {};
    if (arg) {
      a[0] = 1;
    }
    console.log((await foo(a)));
  } catch (err) {
    console.log(err);
  }
};

/***/ })
/******/ ]);

The uglifyjs CLI command executed or minify() options used.

uglify-es -ecma 8 -b -o test.min.js test.js

JavaScript output or error produced.

!function(n) {
    const t = {};
    function e(o) {
        if (t[o]) return t[o].exports;
        const r = t[o] = {
            i: o,
            l: !1,
            exports: {}
        };
        return n[o].call(r.exports, r, r.exports, e), r.l = !0, r.exports;
    }
    e.m = n, e.c = t, e.d = function(n, t, o) {
        e.o(n, t) || Object.defineProperty(n, t, {
            configurable: !1,
            enumerable: !0,
            get: o
        });
    }, e.n = function(n) {
        const t = n && n.__esModule ? function() {
            return n.default;
        } : function() {
            return n;
        };
        return e.d(t, "a", t), t;
    }, e.o = function(n, t) {
        return Object.prototype.hasOwnProperty.call(n, t);
    }, e.p = "", e(e.s = 0);
}([ function(n, t, e) {
    Object.defineProperty(t, "__esModule", {
        value: !0
    }), t.default = async function(n) {
        try {
            const t = {};
            n && (t[0] = 1), console.log(await (t = t, console.log(t))); // TypeError: Assignment to constant variable.
        } catch (n) {
            console.log(n);
        }
        var t;
    };
} ]);

uglify-es generates code t = t, courses "TypeError: Assignment to constant variable."

[Cweili]

uglify-es v3.3.7 is fine.
uglify-es v3.3.8 also produce this bug.

[kzc]

The uglify options provided in the bug report were incorrect.

Reduced test case:

$ cat t2854b.js
(async function bar(arg) {
    function foo(a) {
        return typeof a + 123;
    }
    try {
        const a = {};
        if (arg) {
            a[0] = 1;
        }
        console.log(await foo(a));
    } catch (err) {
        console.log(err);
    }
})();

$ cat t2854b.js | node800
object123

$ cat t2854b.js | bin/uglifyjs -bmc | node800
TypeError: Assignment to constant variable.

Anyway, this is a dup of #2842 and can be closed.

[alexlamsl]

@kzc thanks!