js以变量调用json未知keys的方法

运算符:
let firstProperty = {

foo: 'abc',bar: 123

}::getPropertyByIndex(0);

function getPropertyByIndex(index) {

let keys = Object.keys(this);let key = keys[index];return this[key];

}

或者 getter:
Object.defineProperty(Object.prototype, 'properties', {

get() {    return Object        .keys(this)        .map(key => this[key]);}

});

https://www.jianshu.com/p/575...