js ==运算规则

let a = {
    name: 'zhangsan',
    valueOf(){
        return 100;
    }
};
let b = 100;
console.log(a==b);  //true

let a = {
  value: 1,
  valueOf: function() {
    return this.value++;
  }
};

console.log(a == 1 && a == 2 && a == 3);  // 输出 true