gistfile1.js

var cat = function (hands, feet) {
  this.hands = hands
  this.feet = feet
},

fatcat = function (hands, feet, kg) {
  this.kg = kg
  console.log(this)
  
  cat.call(this, hands, feet)

  // 我在这里以**当前作用域**运行了 cat
  // **相当于** 在这里运行了

  // +function (that, hands, feet) {
  //   that.hands = hands
  //   that.feet = feet
  // }(this, hands, feet)

  // 然后我就多了 this.hands 和 this.feet
  // 

  return this
},

mycat = new fatcat(0, 0, 50);

console.log(mycat)