我在警告框中获取了功能代码，为什么会这样？

Question

When I run this script I get the speak function code in the alert box. It should be "Hello!" not function() {alert("Hello!")}; . I use alert because I seem to like it better over console.log for learning. The script works fine without the speak function.

function person(firstname,lastname,age,eyecolor) {
  this.firstname=firstname;
  this.lastname=lastname;
  this.age=age;
  this.eyecolor=eyecolor;
  this.newlastname=newlastname;
  this.speak=function(){alert("Hello!")};
}

var myFather=new person("John", "Doe", 45, "blue");
var myMother=new person("Sally","Rally", 48,"green");

function newlastname(new_lastname) {
  this.lastname=new_lastname;
}

myMother.newlastname("Doe");
alert(myMother.lastname);
alert(myMother.speak);

Answer 1

Change the last line to

myMother.speak();

For functions that take in strings, (like, alert() ), if you pass in a function, it will take that to mean the source code of the function. So, when you passed myMother.speak into alert , it took the source code, hence the result you were seeing.

(If anyone can expand on this further or provide helpful links, feel free to edit this answer)

Answer 2

I get the function code in the alert box, why is this?

well thats cause your are referencing a function, not calling it, it seems that alert() may be calling the toString() function on the parameter, and calling tostring() on a function reference seems to be returning the source as a string, hence when you alert you get the source, Though this is just a hunch since alert seems to be implemented natively so I can't really say how its implemented.

Nor can I say this behavior is consistent among all browsers.