当且仅当使用它时，如何在 JavaScript 中计算变量? [英] How do I compute a variable in JavaScript if and only if it is used?

问题描述

这就是我现在正在做的事情.

This is what I'm doing right now.

var foo = function() {
  var x = someComplicatedComputationThatMayTakeMoreTime();
  this.foo = function() { return x; };
  return x;
}

它有效，但只有当 foo 被调用为这样的函数时

It works but only if foo is called as a function like so

foo();

但是如果我想将它称为带有值的普通变量呢?我可以将代码修改为

But what if I want to call it as a normal variable with a value? I could modify the code to be

var foo = function() {
  var x = someComplicatedComputationThatMayTakeMoreTime();
  this.foo = x;
  return x;
}

这将允许我只将它作为函数调用一次，然后作为常规变量调用一次.但这仍然不是我想要的.此外，如果它不小心再次作为函数调用，返回错误，它会变得复杂.

That would allow me to only call it once as a function and after that as a regular variable. But it's still not what I want. Plus it gets complicated if it accidentally gets called as a function again, returning an error.

这在 JavaScript 中是否可行?

Is this even possible in JavaScript?

顺便说一句，这是针对 Chrome/Firefox 扩展程序的，因此 IE 兼容性无关紧要.

BTW, this is for a Chrome/Firefox extension, so IE compatibility does not matter.

最终使用 toString 因为 getter 不允许我重新定义整个属性，必须有一个函数与之关联.并且 toString 具有更清晰的语法.

Ended up using toString because getters don't allow me to redefine the whole attribute, a function must be associated with it. And toString has cleaner syntax.

推荐答案

如何使用 toString?

How about using toString?

var foo = function() {
  function someComplicatedComputationThatMayTakeMoreTime() {
        //your calculations
  }
  return {
      toString: function() { 
           return someComplicatedComputationThatMayTakeMoreTime(); 
      }
  }
}

更多关于对象到原始的转换JavaScript

编辑.使用单例(我认为它被称为):

EDIT based on comment. Use a singleton (I think it's called):

myObject.prop = (function(){ 
                  function someComplicatedComputationThatMayTakeMoreTime() {
                   //your calculations
                  }
                  return { 
                    toString: function() { 
                     return someComplicatedComputationThatMayTakeMoreTime(); 
                    } 
                  } 
                })()

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