js 公有方法通过 new Function 方式调用私有方法的问题？

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var Circle = function() {
   var pi = function(){
       return '3.14159';
    };

   this.area = function( str) {
       console.log(eval(str)());    //能正确调用
       console.log(new Function('return '+str));     如何调用??
   };
}
var c= new Circle();
c.area('pi');

function

str

var

调用

10 replies • 2016-05-23 09:27:05 +08:00

littlepanzh

May 22, 2016 via iPhone

LZ 这个写法……可以当面试题了，考察变量作用域……典型的反面教材……

SoloCompany

May 22, 2016 via iPhone

new function 和 eval 完全没区别，都是毫无安全性可言，你漏了执行 function 这一步而已

ftfniqpl

May 22, 2016

@SoloCompany 当我使用 new Function('return '+str).call());的时候,会提示 pi is not defined. 应该是 new Function 的时候需要使用 apply 传入作用域,不知道传啥?

SoloCompany

May 22, 2016 via iPhone

@ftfniqpl 如果是这样的话就说明 new function 不能访问闭包了，建议去查一下 ecma 规范吧

xavierchow

May 22, 2016

Note: Functions created with the Function constructor do not create closures to their creation contexts; they always are created in the global scope. When running them, they will only be able to access their own local variables and global ones, not the ones from the scope in which the Function constructor was called. This is different from using eval with code for a function expression.

-- http://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function

surgit

May 22, 2016

不是 FUNCTION 的问题.
c.area('pi'); 这里的 pi 肯定取不到你构造函数里的静态方法 pi 的.
写代码还是少带点奇技淫巧的好.你这里传 function 作为参数.

magicdawn

May 23, 2016

new Function 只可访问全局变量哦~

var Circle = function() {
var pi = function(){
return '3.14159';
};

var locals = {
pi: pi
};

this.area = function( str) {
return locals[str] && locals[str]();
};
}
var c= new Circle();
c.area('pi');

magicdawn

May 23, 2016

new Function 可以传参哦

sagnitude

May 23, 2016

应该是这儿
http://www.ecma-international.org/ecma-262/5.1/index.html#sec-10.4.2

eval: 10.4.2 的 2.b, 2.c ， eval 会把当前执行 context 设为调用者的 context (VariableEnvironment)
所以能调到局部变量

new Function: 10.4.3 的 5 和 7 ，把当前执行环境设为 NewDeclarativeEnvironment(Function.prototype.[[Scope]])，所以得不到局部变量

orcusfox

May 23, 2016

就没有人给楼主一个正确的姿势吗。。
http://jsbin.com/vefadiyidi/edit?js,console