[英]how to create a custom object in javascript with length property and add and remove functions
I want an object class in javascript that will be written in a separate js file. 我想要将用单独的js文件编写的javascript中的对象类。
This object class will be called Pages . 该对象类将称为Pages 。
the purpose of this object class is for me to manipulate the files property in html5 which is purely read-only. 这个对象类的目的是让我操作html5中的files属性,该属性完全是只读的。
See http://help.dottoro.com/ljslrhdh.php 参见http://help.dottoro.com/ljslrhdh.php
I want the following properties/functions in Pages 我想要页面中的以下属性/功能
The most important characteristics are that: 最重要的特征是:
I do not need code for the various functions. 我不需要各种功能的代码。
I just need a skeleton structure of creating the above custom object class in javascript 我只需要在javascript中创建上述自定义对象类的框架结构
I read Set length property of JavaScript object and thought I need to do it as a function. 我阅读了JavaScript对象的Set length属性,并认为我需要将其作为一个函数来执行。
But then I saw some answers suggesting various improvements like this https://stackoverflow.com/a/6412732/80353 and https://stackoverflow.com/a/6412869/80353 about using Object.create 但是随后我看到了一些答案,提出了各种改进建议,例如关于使用Object.create的https://stackoverflow.com/a/6412732/80353和https://stackoverflow.com/a/6412869/80353
so I am asking for the best template going forward, so that I can add new functions when needed. 因此,我要求最好的模板 ,以便在需要时添加新功能。
Here is the barebones of a structure I have used before, I have only tested this on the latest browsers - however it isn't using any techniques that should cause a problem. 这是我以前使用过的结构的准系统,我只在最新的浏览器上进行过测试-但是,它没有使用任何会引起问题的技术。 The only possible contention would be prototyping an object with an Array.
唯一可能的争用是使用Array制作对象原型。 But I don't see why this wouldn't work in older browsers:
但是我不明白为什么这在较旧的浏览器中不起作用:
<script>
"use strict";
var ArrayLike = (function(){
/// create a static reference to our constructor so that we can
/// add methods to ArrayLike... if we like.
var _static = function(){
/// store some "private" values, and arrayify our arguments
var _args = Array.prototype.slice.call( arguments ),
_private = { byKey:{}, byIndex:{} },
_public = this;
/// make sure the user used the 'new' keyword.
if ( _public instanceof _static ) {
/// if we have arguments then push them onto ourselves
if ( _args.length ) {
_public.splice.apply(_public,[0,0].concat(_args));
}
/// Now that a new instance has been created, switch in an array
/// prototype ready for the next instance.
_static.prototype = new Array();
/// start adding our methods, bare in mind if you wish to
/// stop any of the native array methods from working you'll
/// have to override them here.
_public.add = function( key, value ){
/// store the keys and indexes as references to themselves.
_private.byKey[key] = _public.length;
_private.byIndex[_public.length] = key;
/// use the inherited push function from the array.
_public.push( value );
}
/// an example function to show how get by key would work.
_public.getByKey = function(key){
if ( (key = _private.byKey[key]) || key === 0 ) {
return _public[key] ? _public[key] : null;
}
}
/// easy removeAll thanks to the array prototype.
_public.removeAll = function(){
_public.length = 0;
}
/// here I leave you to flesh out the methods that you 'want'.
_public.removeByKey = function(){
}
/// I'll give you a clue that keeping your array index in order
/// is going to be a manual process, so whenever you delete you
/// will have to reindex.
_private.reIndex = function(){
}
}
}
/// set-up the prototype as an array ready for creation
_static.prototype = new Array();
/// return the function that will be our constructor
return _static;
})();
</script>
The above is a bit odd from the point of view of a normal constructor, because it is constantly modifying it's prototype, this means the following doesn't work as expected: 从普通构造函数的角度来看,上述内容有些奇怪,因为它不断地修改其原型,这意味着以下内容无法按预期工作:
var a = new ArrayLike(1,2,3);
alert( a instanceof ArrayLike ); /// alerts FALSE
The benefits of extending from an Array are quite obvious though as you can now treat a
like any array - so some of your work is done for you by core JS code. 从阵列扩展的优势是相当明显的,虽然你现在可以把
a
像任何阵列-所以你的一些工作是由核心JS代码为你做。 As you are implementing a system that uses keys however, it may be best to override most of the normal array operations so that you can keep a proper track of the keys that are in use in within the structure. 但是,在实现使用键的系统时,最好覆盖大多数常规数组操作,以便您可以正确跟踪结构中正在使用的键。
Anyway hope it helps, I've left you to work out the slightly tricky elements of reindexing the array as it should be straight forward with the way the above is setup. 无论如何希望它会有所帮助,我已经让您解决了重新索引数组的一些棘手元素,因为使用上述设置方法应该很直接。
With regards to setting certain properties to read-only, this is only truly possible in JavaScript 1.8+ - so it wont be backwards compatible to older browsers. 关于将某些属性设置为只读,这仅在JavaScript 1.8+中才真正可能-因此它不会向后兼容旧版浏览器。 You can achieve this using
Object.defineProperty(obj, prop, descriptor)
as mentioned in Felix Kling's comment. 您可以使用Felix Kling的注释中提到的
Object.defineProperty(obj, prop, descriptor)
来实现。 Using this it should be possible to affect things like .length
and make them read-only. 使用它,应该有可能影响
.length
东西并使它们变为只读。 However, the more locked down you make your code, the less flexible and extensible it will be. 但是,编写代码的锁定越多,灵活性和可扩展性就越差。
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