如何在javascript中动态访问本地范围？ [英] How can I access local scope dynamically in javascript?

问题描述

如果你想动态使用全局函数和变量，你可以使用：

If you want to use global functions and variable dynamically you can use:

window[functionName](window[varName]);

是否有可能对本地范围内的变量做同样的事情？

Is it possible to do the same thing for variables in the local scope?

此代码正常运行，但目前使用的是eval，我正在考虑如何做到这一点。

This code works correctly but currently uses eval and I'm trying to think of how else to do it.

var test = function(){
    //this = window
    var a, b, c; //private variables

    var prop = function(name, def){
        //this = window
        eval(name+ ' = ' + (def.toSource() || undefined) + ';');    

        return function(value){
            //this = test object
            if ( !value) {
                return eval('(' + name + ')');
            }
            eval(name + ' = value;')
            return this;
        };

    };

    return {
        a:prop('a', 1),
        b:prop('b', 2),
        c:prop('c', 3),
        d:function(){
            //to show that they are accessible via to methods
            return [a,b,c];
        }
    };
}();

>>>test
Object
>>>test.prop
undefined
>>>test.a
function()
>>>test.a()
1 //returns the default
>>>test.a(123)
Object //returns the object
>>>test.a()
123 //returns the changed private variable
>>>test.d()
[123,2,3]

推荐答案

不，像 crescentfresh 所说。下面是一个没有eval但是有一个内部私有对象的实现的例子。

No, like crescentfresh said. Below you find an example of how to implement without eval, but with an internal private object.

var test = function () {
  var prv={ };
  function prop(name, def) {
    prv[name] = def;
    return function(value) {
      // if (!value) is true for 'undefined', 'null', '0', NaN, '' (empty string) and false.
      // I assume you wanted undefined. If you also want null add: || value===null
      // Another way is to check arguments.length to get how many parameters was
      // given to this function when it was called.
      if (typeof value === "undefined"){
        //check if hasOwnProperty so you don't unexpected results from
        //the objects prototype.
        return Object.prototype.hasOwnProperty.call(prv,name) ? prv[name] : undefined;
      }
      prv[name]=value;
      return this;
    }
  };

  return pub = {
    a:prop('a', 1),
    b:prop('b', 2),
    c:prop('c', 3),
    d:function(){
      //to show that they are accessible via two methods
      //This is a case where 'with' could be used since it only reads from the object.
      return [prv.a,prv.b,prv.c];
    }
  };
}();

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