如何在js中正确使用该方法？

Question

<script>
function Person(gender) {
  this.gender = gender;
}

Person.prototype.sayGender = function()
{
  alert(this.gender);
};

var person1 = new Person('Male');
var genderTeller = person1.sayGender;
genderTeller(); 
</script>

Question:

It shows 'undefined'. what is the problem with the script?

Answer 1

你需要在person1的范围内调用它

genderTell.call(person1);

Answer 2

Evan is right. The scope is window when you call the function. You need to call it on the person. When you retrieve the function like that you only get the function, not the scope.

This also works instead:

function Person(gender) {
    this.gender = gender;
}

Person.prototype.sayGender = function () {
    alert(this.gender);
};

var person1 = new Person('Male');
person1.sayGender(); // <-- calling the function ON "person1" directly

FIDDLE