Javascript 超时无法捕获类中的值

Question

function MyClass(){
  this.field1 = "Field in MyClass";
}
MyClass.prototype.print = function() {
  console.log("print in MyClass:" + this.field1);
}
function useMyClassPrint() {
  var mc = new MyClass();
  mc.print(); 
  setTimeout(mc.print, 10);
  setTimeout("mc.print()", 10);
}

我得到这些结果：

mc.print(); // this one is easy, it returns "print in MyClass:Field in MyClass"  
// but ...  
setTimeout(mc.print, 10); // "print in MyClass:undefined" why?!  
setTimeout("mc.print()", 10); // runtime error?!@@  

Answer 1

function MyClass(){
  this.field1 = "Field in MyClass";
}
MyClass.prototype.print = function() {
  console.log("print in MyClass:" + this.field1);
}
  var mc = new MyClass();
  mc.print(); /*ok*/
  setTimeout(mc.print, 10); /*it's just a reference to function*/
  setTimeout(mc.print.bind(mc),10);/*binded*/

当您定义时

function MyClass(){
  this.field1 = "Field in MyClass";
}

字段 1

是在实例化类时设置的。字段 1 不是常量。

在控制台中试用：

MyClass.field1 -> /*undefined*/
new MyClass().field1 -> /*Field in MyClass*/

setInterval(( 函数接收一个函数：

setTimeout(mc.print, 10);

mc.print 只是对函数的引用，没有对"mc"实例的引用。