js 對(duì)象訪問(wèn)器屬性問(wèn)題

想請(qǐng)問(wèn)下 js 對(duì)象的命名訪問(wèn)器屬性與通過(guò) defineProperty 設(shè)置 getter 和 setter 函數(shù)的區(qū)別：

 a = {
    name: 'aaa',
    get myName() {
        return this.name
    }
}
a.myName //'aaa'

b = {
    name: 'bbb'
}
Object.defineProperty(b, 'myName', {
    get: function() {
        return this.name
    },
    set: function(newName) {
        this.name = newName
    }
})
b.myName //'bbb'