JavaScript Babel 编译 ES6 的 class extends Array 时，无法获取方法，求助
代码如下
class MyCoolArray extends Array {
first() { return this[0];}
}
var a = new MyCoolArray(1,2,3);
console.log(a.first());// get error 'a.first is not a function'
谁知道为什么 first 无法执行？谢谢
Built-in classes such as Date, Array, DOM etc cannot be properly subclassed due to limitations in ES5 (for the es2015-classes plugin). You can try to use babel-plugin-transform-builtin-extend based on Object.setPrototypeOf and Reflect.construct, but it also has some limitations. https://babeljs.io/docs/usage/caveats/