Question

我正在尝试理解对象和函数，这是我的代码：

function house(roof) {
  this.roof = roof;
  this.roofdescrip = describehouse();
}

function describehouse(){
  var z = this.roof;
  x="The house has a roof.";
  y="The house does not have a roof.";
  if(z===true){return x;}
  else{return y;}

  }

var myhouse = new house(true);



document.write(myhouse.roofdescrip);

始终返回

The house does not have a roof.

我是否将参数更改为true或false。为什么呢？

Answer 1

那是因为Match_number,Winner,Winner_Score,Loser_score 1,Red,2,1 2,Blue,3,2 3,Red,4,1 etc...函数中的this运算符指向窗口对象，describehouse()等于roof，请尝试传递{{1}作为参数。像这样的东西

undefined

Answer 2

问题与范围有关。在您的情况下，this函数中的describehouse实际上是window对象。如果您尝试在函数内部记录this.roof，则会获得undefined。 undefined被认为是错误的，这就是你总能获得相同结果的原因。

要使代码正常工作，您需要将函数绑定到对象，然后调用函数。

function house(roof) {
  this.roof = roof;
  this.roofdescrip = describehouse.bind(this);
}


function describehouse(){
  var z = this.roof;
  console.log(this)
  x="The house has a roof.";
  y="The house does not have a roof.";
  if(z===true){return x;}
  else{return y;}

  }

var myhouse = new house(true);

document.write(myhouse.roofdescrip());

我在这里采用另一种方式来做到这一点。

class House {
  constructor(roof) {
    this.roof = roof
  }

  describeHouse() {
    const verb = this.roof ? "has" : "does not have"
    return `The house ${verb} a roof.`
  }
}

const myHouse = new House(true)
const otherHouse = new House(false)
console.log(myHouse.describeHouse()) // "The house has a roof."
console.log(otherHouse.describeHouse()) // "The house does not have a roof."

具有布尔值的比较运算符始终返回false

2 个答案: