我如何得到“this = this”在原型工作 [英] how do i get "this = this" in prototype working
问题描述
好看，所以我知道弄乱原型是不好的做法，但无论如何......
Ok peep's so I know it's bad practice to mess with prototypes but here it is anyway...
Array.prototype.rev=
function(){
this.reverse();
}
工作正常！按预期更新源数组变量 ary ，例如：
Works fine! Updates the source array variable, ary, as expected eg:
ary = [123, 456];
ary.rev();
// result: ary == [456, 123]
为 String 写一个类似的属性时出现问题。
My problem comes when writing a similar property for String.
什么我想做的就是这样...
What I would like to do is something like this...
String.prototype.rev=
function(){
this.split('');
this.reverse();
this.join('');
}
看起来很简单吧！拆分字符串，反转它，然后将它连接在一起，这样原来的字符串变量 str 就像它以前的自身一样，与
Seems simple enough right! Split the string, reverse it, and join it back together so the original string variable, str, is a reverse of it's former self, as was with the ary above!
事情是：虽然 this.split（）已经调用它需要存储为变量，即：
Thing is: Although this.split() has been called it needs to be stored as a variable, ie:
split = this.split('');
还有 this = this 问题...
现在拆分已定义，它将注意力从编辑源变量上移开，并不像我在函数结尾处所说的那样：
Now split is defined, it takes the focus away from editing the source variable and it's not like I can just say at the end of the function:
this = split;
作为这个是'不可变'还是什么它们是否意味着它是静态的且不可改变的？
As this is 'immutable' or what ever it is when they mean it is static and unchangeable?
str = 'abc'
我希望能够说 str.rev（）而不是 str = str .rev（）并获得 str ='cba'的结果其中 str ==='cba'，抓住我的漂移？！
I want to be able to say str.rev() not str = str.rev() and get the result of str = 'cba' where str === 'cba', catch my drift?!
所有的解决方法和学费欢迎窥视，我只是问你知道你在说什么回合。 thx
All work-around's and tuition welcome peep's, I just ask that u know what ur talkin' 'bout. thx
推荐答案
为
String <编写类似属性时出现问题/ code> ...
My problem comes when writing a similar property for
String...
这里的主要问题是JavaScript中的字符串不可变 ;你不能改变一个字符串。因此，不可能定义一个行为如下的 rev 方法：
The main issue here is that strings are immutable in JavaScript; you cannot change a string in place. Because of that, it's impossible to define a rev method that would behave like this:
var a = 'abc';
a.rev(); // <== This can't work this way
console.log(a); // cba
相反，你的 rev 应该做所有其他 String 方法：返回带有更新的新字符串。
Instead, your rev should do what all other String methods do: Return a new string with the updates.
第二个问题是您的 rev 方法中的代码不起作用，因为您没有保存 this.split等内容的结果（''）; 在任何地方，但 split 的方式有效，返回带有条目的数组。
A secondary issue is that your code in your rev method doesn't work, because you're not saving the results of things like this.split(''); anywhere, but the way split works, it returns an array with the entries.
这是一个解决这两个问题的 rev 版本：
Here's a version of rev that addresses both issues:
String.prototype.rev=
function(){
return this.split('').reverse().join('');
};
然后：
var a = 'abc'.rev();
console.log(a); // cba
示例：
String.prototype.rev = function(){
return this.split('').reverse().join('');
};
var a = 'abc'.rev();
snippet.log(a);
<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>
这是所有标准字符串方法（ toLowerCase ，替换， substring ，...）工作，返回结果。
This is how all of the standard string methods (toLowerCase, replace, substring, ...) work, by returning the result.
所有在线版本可能不太清晰（并且很难调试），这里是拆分版本清晰度：
The all-on-one-line version might not be hyper clear (and is hard to debug), here's the split-apart version for clarity:
String.prototype.rev=
function(){
var characters = this.split('');
characters.reverse();
return characters.join('');
};
（注意 Array＃reverse 撤销就地放置和返回数组引用;它还返回数组引用的事实是使一体化版本成为可能的原因。）
(Note that Array#reverse reverses the array in place and returns the array reference; the fact it also returns the array reference is what makes the all-in-one-line version possible.)
附注：如果您打算使用原型，请考虑使用 Object.defineProperty 而不是仅仅分配：
Side note: If you're going to play around with prototypes, consider using Object.defineProperty rather than just assigning:
Object.defineProperty(String.prototype, "rev", {
value: function() { ... }
});
...以便新属性不可枚举（不显示在 for-in 循环）。使用 String 并不重要，但很多人仍然错误地使用 for-in 用于循环遍历数组，所以......
...so that the new properties are non-enumerable (don't show up in for-in loops). Doesn't matter that much with String, but a lot of people still incorrectly use for-in for looping through arrays, so...
示例：
Object.defineProperty(String.prototype, "rev", {
value: function(){
return this.split('').reverse().join('');
}
});
var a = 'abc'.rev();
snippet.log(a);
<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>
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