javascript 如何在javascript中制作“点函数”
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How to make a "dot function" in javascript
提问by Oliver Ni
I'm trying to define a "dot function" where there are no parameters but has a .and a string or number before it like these:
我试图定义一个“点函数”，其中没有参数，但.在它之前有一个和一个字符串或数字，如下所示：
.toUpperCase()
.toLowerCase()
.indexOf()
.charAt()
.substring()
.toUpperCase()
.toLowerCase()
.indexOf()
.charAt()
.substring()
You do 2..toString, not toString(2).
你有2..toString，没有toString(2)。
How do you define one of them?
你如何定义其中之一？
And why when I type 4..toString()it returns function toString() {[native code]}?
为什么当我输入4..toString()它时返回function toString() {[native code]}？
采纳答案by Paul Draper
Defining a "dot function" is easy. Here's how you can define it on a single object.
定义“点函数”很容易。以下是在单个对象上定义它的方法。
var a = {}, or a = function() {}, or a = [], etc.
a.dotFunction = function() { return 'hi'; }
console.log(a.dotFunction());
If you want to define it on all instances of a "class", use prototype.
如果要在“类”的所有实例上定义它，请使用prototype.
function someClass() {
}
someClass.prototype.dotFunction = function() { return 'hi'; };
console.log(new someClass().dotFunction());
You can even do this on built-in types (some, like Prototype.js, do this, though most recommended against it).
您甚至可以在内置类型上执行此操作（有些，例如 Prototype.js，执行此操作，但大多数人建议不要这样做）。
Number.prototype.dotFunction = function() { return 'hi'; };
console.log((0).dotFunction());
回答by p.s.w.g
I'd strongly recommend not trying to replace any built-in methods, however, you're free to define your own methods however you like.
我强烈建议不要尝试替换任何内置方法，但是，您可以随意定义自己的方法。
You can do this by attaching the method to the Numberor Stringtype's prototype:
您可以通过将方法附加到Number或String类型的原型来做到这一点：
Number.prototype.foo = function(n) { return this * n; };
String.prototype.bar = function(n) { return this.length * n; };
alert(4..foo(2)); // 8
alert("4".bar(2)); // 2
Further Reading
进一步阅读
回答by HMR
I'll give it a shot because nobody mentioned that you can already do this without having to define anything yourself.
我会试一试，因为没有人提到你已经可以做到这一点，而不必自己定义任何东西。
A thing to take care of is if you have a number you have to place 2 dots after it where as if you have a function that returns a number or a variable that holds one you don't:
需要注意的是，如果您有一个数字，则必须在其后放置 2 个点，就像您有一个返回数字的函数或一个包含您没有的数字的变量一样：
1..toString()
.indexOf("1")//<=returns number 0
//even though a number is returned we only need one dot here
.toString();//<="0"
var num = 1234;
num.toString()//<=one dot
.indexOf("23");//<=1
Your example would already work but since indexOfwould return a number if you give it an argument that makes sense and a number doesn't have a charAtmethod.
你的例子已经可以工作了，但是indexOf如果你给它一个有意义的参数并且一个数字没有charAt方法，它就会返回一个数字。
"hello".toUpperCase()
.toLowerCase()
.indexOf("h")//<=returns a number
//number has no charAt method
.toString()
.charAt(0)
.substring(0);//<="0"
