Javascript 如何在构造函数中设置javascript私有变量？
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How to set javascript private variables in constructor?
提问by Click Upvote
Say I have a javascript function/class called Fooand it has a property called bar. I want the value of barto be supplied when the class is instantiated, e.g:
假设我调用了一个 javascript 函数/类Foo，它有一个名为bar. 我希望在bar实例化类时提供的值，例如：
var myFoo = new Foo(5);
would set myFoo.barto 5.
将设置myFoo.bar为 5。
If I make bara public variable, then this works, e.g:
如果我创建bar一个公共变量，那么这有效，例如：
function Foo(bar)
{
this.bar = bar;
}
But if I want to make it private, e.g:
但是，如果我想将其设为私有，例如：
function Foo(bar)
{
var bar;
}
Then how would I set the value of the private variable barsuch that its available to all internal functions of foo?
那么我将如何设置私有变量的值bar，使其可用于所有内部函数foo？
回答by jfriend00
One of the best tutorials on private and protected access in javascript is here: http://javascript.crockford.com/private.html.
关于 javascript 中私有和受保护访问的最佳教程之一在这里：http: //javascript.crockford.com/private.html。
function Foo(a) {
var bar = a; // private instance data
this.getBar = function() {return(bar);} // methods with access to private variable
this.setBar = function(a) {bar = a;}
}
var x = new Foo(3);
var y = x.getBar(); // 3
x.setBar(12);
var z = x.bar; // not allowed (x has no public property named "bar")
回答by Digital Plane
You have to put all functions that need to access the private variable inside the constructor:
您必须将所有需要访问私有变量的函数放在构造函数中：
function Foo(bar)
{
//bar is inside a closure now, only these functions can access it
this.setBar = function() {bar = 5;}
this.getBar = function() {return bar;}
//Other functions
}
var myFoo = new Foo(5);
myFoo.bar; //Undefined, cannot access variable closure
myFoo.getBar(); //Works, returns 5
回答by Paul
function Foo(b)
{
var bar = b;
this.setBar = function(x){
bar = x;
}
this.alertBar = function(){
alert(bar);
}
}
var test = new Foo(10);
alert(test.bar); // Alerts undefined
test.alertBar(); // Alerts 10
回答by marksyzm
One way I can think of is to use a closure that's assigned to a name and returns a new object. You would pass in any arguments to the constructor through the call to the closure. That would end up being something like the following:
我能想到的一种方法是使用分配给名称并返回新对象的闭包。您可以通过调用闭包将任何参数传递给构造函数。这最终将类似于以下内容：
var fooFactory = function (a, b) {
var c = 5,
d = 6,
foo;
foo = function (a, b) {
this.a = a;
this.b = b;
this.bar();
}
foo.prototype.bar = function () {
//do something with c and d
this.c = c + d;
}
foo.prototype.getC = function () {
return c;
}
foo.prototype.getD = function () {
return d;
}
return new foo(a, b);
};
This way, a and b are always declared uniquely. You would then construct your object like so:
这样， a 和 b 总是被唯一声明。然后你可以像这样构造你的对象：
var obj = fooFactory(1, 2);
//obj contains new object: { a: 1, b: 2, c: 11 }
console.log(obj.getC());
//returns 5
回答by Nitin Jadhav
If you are willing to use ES2015 classes,
如果你愿意使用 ES2015 类，
with ESNext, you can use Javascript private variableslike this:
使用 ESNext，您可以像这样使用Javascript 私有变量：
class Foo {
#bar = '';
constructor(val){
this.#bar = val;
}
otherFn(){
console.log(this.#bar);
}
}
Private field #bar is not accessible outside Foo class.
私有字段 #bar 在 Foo 类之外不可访问。
回答by Peter Schweitzer Jr
I recently had a similar issue but wanted to use accessor properties also. Below is a Foo(Bar) example based on what I came up with for a solution. This example is trivial but can easily be expanded upon using more complex get/set functions.
我最近遇到了类似的问题，但也想使用访问器属性。下面是一个基于我想出的解决方案的 Foo(Bar) 示例。这个例子是微不足道的，但可以很容易地扩展使用更复杂的 get/set 函数。
function Foo(Bar){
Object.defineProperty(this,"bar",{get:function(){return Bar},set:function(val){Bar=val}});
}
x=new Foo(3);
y=x.bar; //3
x.bar++; //x.bar==4
