SOURCE

// Object.keys:返回一个由一个给定对象的自身可枚举属性组成的数组
Object.keys = Object.keys || function keys(object) {
    if(object === null || object === undefined) {
        throw new TypeError('Cannot convert undefind or null to object')
    }
    let result = []
    if(isArrayLike(object) || isPlainObject(object)) {
        for(let key in object) {
            object.hasOwnProperty(key) && (result.push(key))
        }
    }
    console.log(result)
    return result
}