我该如何处理多个浏览器脚本制作到后端服务相同的调用 [英] How do I handle multiple browser scripts making the same calls to the back-end service
问题描述
我有一个网页,它的所有不同部分需要同样的后端数据。每个分离,所以它们每个最终最终使得向后端相同的呼叫。
I have a web page where different parts of it all need the same back-end data. Each is isolated, so they each end up eventually making the same calls to the back-end.
什么是避免到Web服务器的调用,当一个已在进行中,由同一网页?
What is the best way to avoid making a call to the web server when one is already in progress and initiated by a different piece of code on the same web page?
下面是一个例子。我将使用的setTimeout来模拟一个异步调用。
Here's an example. I'll use setTimeout to simulate an asynchronous call.
让我们假设有一个返回的联系人列表,这基本上是字符串在本实施例的简单阵列的异步函数:
Let's assume there's an async function that returns the list of contacts, which is basically a simple array of strings in this example:
var getContacts = function() {
log('Calling back-end to get contact list.');
return new Promise(function(resolve, reject) {
setTimeout(function() {
log('New data received from back-end.');
resolve(["Mary","Frank","Klaus"]);
}, 3000);
});
};
现在,让我们来创建三个不同的功能,每个调用上面的函数用于不同的目的。
Now, let's create three separate functions that each call the above function for different purposes.
dump出来的联系人列表:
Dump out the list of contacts:
var dumpContacts = function() {
getContacts().then(function(contacts) {
for( var i = 0; i < contacts.length; i++ ) {
log( "Contact " + (i + 1) + ": " + contacts[i] );
}
});
};
确定一个特定的接触是在列表中:
Determine if a particular contact is in the list:
var contactExists = function(contactName) {
return getContacts().then(function(contacts) {
return contacts.indexOf(contactName) >= 0 ? true : false;
});
};
获取第一个联系人的名称:
Get the name of the first contact:
var getFirstContact = function() {
return getContacts().then(function(contacts) {
if ( contacts.length > 0 ) {
return contacts[0];
}
});
};
和这里有一些例子code使用这三个功能:
And here is some example code to use these three functions:
// Show all contacts
dumpContacts();
// Does contact 'Jane' exist?
contactExists("Jane").then(function(exists){
log("Contact 'Jane' exist: " + exists);
});
getFirstContact().then(function(firstContact){
log("first contact: " + firstContact);
});
以上程序使用一个全局日志()函数。的console.log()可以被代替使用。上述日志()函数日志的浏览器窗口,并实现如下:
The above routines make use of a global log() function. console.log() could be used instead. The above log() function log's to the browser window and is implemented as follows:
function log() {
var args = Array.prototype.slice.call(arguments).join(", ");
console.log(args);
var output = document.getElementById('output');
output.innerHTML += args + "<br/>";
}
和需要在HTML以下内容:
and requires the following in the html:
<div id='output'><br/></div>
在运行上述code,您将看到:
When the above code is run, you will see:
Calling back-end to get contact list.
和
New data received from back-end.
三次,这是不必要的。
这怎么能解决吗?
这样品是在Plunker可以执行:
http://plnkr.co/edit/6ysbNTf1lSf5b7L3sJxQ?p=$p$pview一>
This sample is on Plunker can be executed: http://plnkr.co/edit/6ysbNTf1lSf5b7L3sJxQ?p=preview
推荐答案
只是缓存结果的函数进行调用:
Just cache the result in the function making the call:
function cache(promiseReturningFn){
var cachedVal = null; // start without cached value
function cached(){
if(cachedVal) return cachedVal; // prefer cached result
cachedVal = promiseReturningFn.apply(this, arguments); // delegate
return cachedVal; // after we saved it, return it
}
cached.flush = function(){ cachedVal = undefined; };
return cached;
}
这有失败对于那些空但除此之外,它得到很好的完成工作实际结果的警告。
This has the caveat of failing for actual results that are null but otherwise it gets the job done nicely.
您现在可以缓存任何承诺返回函数 - 只以上的版本缓存忽略的参数 - 但你可以构造一个类似,有一个地图和缓存根据不同的参数太多 - 但让我们专注于您的使用情况
You can now cache any promise returning function - the version above only caches ignoring arguments - but you can construct a similar one that has a Map and caches based on different arguments too - but let's focus on your use case.
var getContactsCached = cache(getContacts);
getContactsCached();
getContactsCached();
getContactsCached(); // only one async call ever made
缓存方法是居然连不相关的承诺 - 它是所有需要的功能,并缓存它的结果 - 你可以用它来做什么。事实上,如果您使用的是像库下划线你可以使用 _。memoize的
来为你做了。
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