JavaScript Object的defineProperty / getOwnPropertyDescriptor

getOwnPropertyDescriptor and defineProperty

 function def (obj, key, val, enumerable) {
  Object.defineProperty(obj, key, {
    value: val,
    enumerable: !!enumerable,
    writable: true,
    configurable: true
  })
}

const obj = {}
def(obj,'name','leslie',true)
def(obj,'age',18,false)
def(obj,'company','ibm',true)
//  测试 enumerable
for(let [key,value]  of Object.entries(obj)){
    //  只会打印出 name 和 company属性
    //  因为 age 是不可枚举的属性
    console.info(`${key}:${value}`)
}
// 测试 getOwnPropertyDescriptor
const property = Object.getOwnPropertyDescriptor(obj,'age')
/*
{
  configurable: true,
  enumerable: false,
  value: 18,
  writable: true,
}
*/
console.info(property)

//  对象属性获取，兼容模式
const name = obj && obj.name
const test = obj && obj.test || 'test'
console.info(name) //  leslie
console.info(test) //  test