Javascript 是什么让这两个功能';公共';和';私人';分别是什么意思?
这两个函数来自我正在学习的课程()。代码和注释来自课程提供商:Javascript 是什么让这两个功能';公共';和';私人';分别是什么意思?,javascript,oop,private,public,Javascript,Oop,Private,Public,这两个函数来自我正在学习的课程()。代码和注释来自课程提供商: /* This is the publicly accessible image loading function. It accepts * an array of strings pointing to image files or a string for a single * image. It will then call our private image loading function accordingly.
/* This is the publicly accessible image loading function. It accepts
* an array of strings pointing to image files or a string for a single
* image. It will then call our private image loading function accordingly.
*/
function load(urlOrArr) {
if(urlOrArr instanceof Array) {
/* If the developer passed in an array of images
* loop through each value and call our image
* loader on that image file
*/
urlOrArr.forEach(function(url) {
_load(url);
});
} else {
/* The developer did not pass an array to this function,
* assume the value is a string and call our image loader
* directly.
*/
_load(urlOrArr);
}
}
/* This is our private image loader function, it is
* called by the public image loader function.
*/
function _load(url) {
if(resourceCache[url]) {
/* If this URL has been previously loaded it will exist within
* our resourceCache array. Just return that image rather
* re-loading the image.
*/
return resourceCache[url];
} else {
/* This URL has not been previously loaded and is not present
* within our cache; we'll need to load this image.
*/
var img = new Image();
img.onload = function() {
/* Once our image has properly loaded, add it to our cache
* so that we can simply return this image if the developer
* attempts to load this file in the future.
*/
resourceCache[url] = img;
/* Once the image is actually loaded and properly cached,
* call all of the onReady() callbacks we have defined.
*/
if(isReady()) {
readyCallbacks.forEach(function(func) { func(); });
}
};
/* Set the initial cache value to false, this will change when
* the image's onload event handler is called. Finally, point
* the image's src attribute to the passed in URL.
*/
resourceCache[url] = false;
img.src = url;
}
}
为什么load()
是“公共可访问的”,而\u load()
是“私有的”?在这种情况下,公共/私人是什么意思
如果需要,完整文件位于它是私有的,因为无法直接调用它。。。见第105行:
window.Resources = {
load: load,
get: get,
onReady: onReady,
isReady: isReady
};
由于该方法是在作用域中声明的,因此它在其他任何地方都不可用
您可以看到,代码写在:
(function() {
...
})()
它强制将任何函数声明或变量声明附加到当前范围。如果没有此选项,变量将附加到最近的当前对象(通常是窗口)。因此,永远不会导出\u load
,调用它的唯一方法是调用资源
对象中窗口
上导出的方法之一
- 公共是指可以从外部调用某些内容
- 私密是指只能从内部调用某些内容
在Javascript中,私有属性通常隐藏在一个作用域中,该作用域仅对在该作用域中创建的函数可用。“Public”意味着可以从任何地方调用它。“Private”表示只能从包含此函数的文件中访问它。还要注意的是,它说“Public”函数调用“Private”函数,因此当您运行“Public”函数时,它仍然运行相同的代码。此外,请注意,许多人使用初始下划线(“”)来表示私有数据。这仅仅是一个约定,它本身实际上并不强制私有访问。但有些人把它作为区分公共和私人的唯一机制。