JavaScript：hasOwnProperty vs dot语法

Question

想象一下有一个对象：foo = {"bar": 1}

使用hasOwnProperty优于dot-syntax来检查bar对象中的foo属性是否有任何好处：

if (foo.hasOwnProperty('bar') {
  // do something
}

VS

if (foo.bar) {
  // do something
}

另外：

• 如果foo["bar"]是undefined？
会有什么结果
• 如果foo undefined
该怎么办？

Answer 1

看看这个例子，

＆＃13;

＆＃13;

Object.prototype.baz = 100;
var foo = {"bar": 1}

// will be false because in foo object there is no baz property 
// hasOwnProperty checks that the object has the specified property 
// and does not check that property in the prototype chain
if (foo.hasOwnProperty('baz')) {
  console.log('foo.hasOwnProperty("baz")');
}


//  will be true because baz property will be found 
//  in parent object through prototype chain
if (foo.baz) {
  console.log('foo.baz');
}

＆＃13;

＆＃13;

＆＃13;