从函数声明的堆栈中访问变量
Posted
tags:
篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了从函数声明的堆栈中访问变量相关的知识，希望对你有一定的参考价值。
在javascript中创建Stack的接口 - 使用函数样式而不是原型或伪古典样式时，下面的“storage”和“count”变量应分别为someInstance.storage和someInstance.count，以便它们可以在这个堆栈的实例以后呢？
随着变量现在被声明，一旦我们通过执行函数创建和堆栈实例，我们将失去访问权以查看计数（大小）和存储（堆栈中的属性）。
声明我们稍后需要使用功能创建模式访问的属性（而不是方法）的最佳方法是什么？
谢谢！
var Stack = function(){
var someInstance = {};
var storage = {};
var count = 0;
someInstance.push = function(value){
storage[count++] = value;
};
someInstance.pop = function(){
if(count){
var popped = storage[--count];
}
delete storage[count];
return popped;
};
someInstance.size = function(){
return count;
};
return someInstance;
};
var stack = Stack();
答案
下面提到的私有变量可以在closure的javascript中进行研究。
参考：https://developer.mozilla.org/ko/docs/Web/JavaScript/Guide/Closures
var Stack = function(){
// PUBLIC
var someInstance = {};
// PRIVATE: Attach _ to private variables. (just implicit rule.)
var _storage = {};
var _count = 0;
someInstance.push = function(value){
storage[_count++] = value;
};
someInstance.pop = function(){
if(_count){
var popped = storage[--_count];
}
delete storage[_count];
return popped;
};
someInstance._size = function(){
return _count;
};
// if you assign public variable, you can access!!!
someInstance.size = _size;
someInstance.count = _count;
return someInstance;
};
var stack = Stack();
另一答案
您可以在someInstance对象中添加getter和setter（由闭包提供），如下所示：
Object.defineProperty(someInstance, "count", {
get: function() {
return count;
},
set: function(value) {
count = value;
}
});
如果您希望能够获取值而不设置它，则可以省略set部分。
例：
var Stack = function(){
var someInstance = {};
var storage = {};
var count = 0;
Object.defineProperty(someInstance, "count", {
get: function() {
console.log("getter called");
return count;
},
set: function(value) {
console.log("setter called");
count = value;
}
});
return someInstance;
};
var stack = Stack();
console.log(stack.count);
stack.count = 55;
console.log(stack.count);另一答案
storage和count是否应该是someInstance.storage和someInstance.count取决于你希望这个实例的用户如何工作它。这有点基于意见。我的观点是堆栈不应该允许用户使用someInstance.count = 10之类的东西来改变计数，因为这样会破坏它。
我个人会让count和storage私有，这将防止直接访问可能发生的意外错误。一个很好的方法是在闭包中捕获它们并为count提供一个getter，这样你仍然可以读取计数，但不能改变它。就像是：
var Stack = function(){
let storage = [], count = 0; // these will be caputured as a closure
return {
// the returned object will have push, pop, and a count getter
push(v) {
storage.push(v)
count++
},
pop() {
if (count) count--
return storage.pop()
},
get count(){ // allow reading of count
return count
}
}
}
var stack = Stack();
stack.push("hello");
stack.push("goodby");
stack.count = 10 // has no effect
console.log(stack.count) // count is still 2
console.log(stack.pop())
console.log(stack.count)
console.log(stack.pop())
console.log(stack.count)另一答案
var Stack = function(){
let storage = [], count = 0; // these will be caputured as a closure
return {
// the returned object will have push, pop, and a count getter
push(v) { //method
storage.push(v)
count++
},
pop: function() {
if (count) count--
return storage.pop()
},
get count(){ // allow reading of count
return count
},
get insidebox(){ // allow reading of count
return storage
},
callprice:function(cnt){
var price=cnt*100;
return price;
}
}
}
Stack.prototype.price2 = function() {
return "testpr";
};
var sb = Stack();
console.log(sb.count);
sb.push('paint');
console.log(sb.insidebox);
console.log(sb.count);
sb.push('Sharee');
console.log(sb.insidebox);
sb.push('Shirt');
sb.push('shoes');
console.log(sb.insidebox);
sb.pop();
console.log(sb.insidebox);
console.log(sb.count);
console.log(sb.callprice(sb.count));另一答案
function Person(first, last, age, eye) {
this.firstName = first;
this.lastName = last;
this.age = age;
this.eyeColor = eye;
}
Person.prototype.nationlity='Indian';
Person.prototype.fullname = function() {
return this.firstName + " " + this.lastName
};
var myFather = new Person("Lalji", "Maurya", 50, "blue");
console.log(myFather.fullname());
console.log(myFather);
console.log(myFather.nationlity);
var myBrother = new Person("Ashish", "Maurya", 28, "black");
console.log(myBrother.fullname());
console.log(myBrother);
console.log(myBrother.nationlity); 以上是关于从函数声明的堆栈中访问变量的主要内容，如果未能解决你的问题，请参考以下文章