Transpile to ES5 not working for imported modules

[mengzhen94]

I am importing js classes as modules to other js files and import them to my angular 5 ts project like this:

if (typeof module !== 'undefined') {
  var CPE = {};
  CPE.a1 = require('./a1');
}

CPE.a2 = class a2 extends a1 {}

if (typeof module !== 'undefined') {
  var CPE = {};
  CPE.a3 = require('../a/a3.js');
  CPE.a4 = require('../a/a4.js');
}

CPE.a5 = class Curve{
  constructor (params = {}) {
    params.className = 'a5';

    super(params);

    this.modifiers = {
      a3: new CPE.a3(this),
      a4: new CPE.a4(this)
    };
  }
 ....

In ts file:

import * as CPE from '../../../../../app/aa/a/a1';

When ng build --prod and transpile to ES5, some of js class are still 'class', not transpiled at all. Also weird thing is each time the files not transpiled properly are not same.
Here is the file main.XXX.bundle.js after build:

if (typeof module !== 'undefined') {
  var CPE = {};
  CPE.a3 = require('../a/a3.js');
  CPE.a4 = require('../a/a4.js');
}

CPE.a5 = class Curve{
  constructor (params = {}) {
    params.className = 'a5';

    super(params);

    this.modifiers = {
      a3: new CPE.a3(this),
      a4: new CPE.a4(this)
    };
  }
 ....

it is literally the original js class, not transpiled at all.

Versions

tsconfig,json:

{
  "compileOnSave": false,
  "compilerOptions": {
    "allowJs": true,
    "outDir": "./dist/out-tsc",
    "sourceMap": true,
    "baseUrl": "./src/",
    "declaration": false,
    "moduleResolution": "node",
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "target": "es5",
    "types": [
      "underscore"
    ],
    "typeRoots": [
      "node_modules/@types"
    ],
    "lib": [
      "es2017",
      "dom"
    ],
    "plugins": [
      { "name": "tslint-language-service"}
    ]
  }
}

package.json

  "devDependencies": {
    "@angular/cli": "1.7.4",
    "@angular/compiler-cli": "^5.0.0",
    "@angular/language-service": "^5.0.0",
...

The log given by the failure

Not build errors. But the 'class' keyword fails on IE11

Is there anyone has clue what is happening and how to fix it? Thanks.

[clydin]

The CLI does not transpile Javascript code. Third-party code is expected to be in the appropriate format.
For project files that are javascript and imported in TypeScript files, the allowJs option may allow the javascript files to be processed by the TypeScript compiler. Please note that this is untested and not officially supported.

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