Object你真的知道它吗

Object.defineProperty

    let obj = {
        a: 1,
        b: 2
    };
    Object.prototype.c = 3;
    Object.defineProperty(obj, 'd', {
        enumerable: false
    });
    for (let key in obj) {
        console.log(key);
    }

//输出 :
a 
b 
c