Javascript承诺中的动态链接 [英] Dynamic Chaining in Javascript Promises

问题描述

如何在Javascript Promises中执行动态链接，我一直只看到调用的硬编码，例如。，（promise）.then（request / functionName） ）.then（request / functionName）

How can I perform dynamic chaining in Javascript Promises, all the time I have seen only hardcoding of the calls for eg., (promise).then(request/functionName).then(request/functionName)

推荐答案

一种选择是利用对象的属性和通过字符串调用它们的能力。

One option is to utilize the properties of objects and the ability to invoke them via strings.

我写了一个小样本这里并在下面发布。

I wrote a small sample Here and posted it below.

这个想法是你有一套你希望在某个命名空间或对象中运行的函数集，就像我在'myNamespace'中所做的那样：

The idea is that you have the set of functions that you wish to run set in some namespace or object, as I did in 'myNamespace':

myNamespace = {
    "A": function() {return "A Function";},
    "B": function() {return "B Function";},
    "C": function() {return "C Function";}
}

然后你的主要承诺会以某种方式运行（通过输入，ajax，提示等）你会得到字符串值o f你想要运行的功能，直到运行时才知道：

Then your main promise would run and somehow (via inputs, ajax, prompts, etc.) you would get the string value of the function you want to have run, which isn't known until runtime:

我的主承诺使用提示来获取用户的来信：

My main promise uses a prompt to get a letter from the user:

var answer = prompt('Starting.  Please pick a letter: A,B,C');
        if(myNamespace[answer] === undefined)
        {
            alert("Invalid choice!");
            reject("Invalid choice of: " + answer);
        }
        else
        {
            resolve(answer);
        }

在下一个'然后'我使用该值（通过resolve函数传递） ）调用函数：

In the next 'then' I use that value (passed via the resolve function) to invoke the function:

.then(function(response) {
        funcToRun = myNamespace[response]();})

最后，我输出到html动态函数调用的结果，我使用了一些递归有趣的是使它更具互动性并证明它是动态的：

Finally, I output to html the result of my dynamic function call and I use some recursive fun to make it more interactive and demonstrate that it is dynamic:

.then(function(){
        document.getElementById('result').innerHTML = funcToRun;})
    .then(function(){
        if(prompt("Run Again? (YES/NO)")==="YES")
        {
            doWork();
        }
    });

myNamespace = {
    "A": function() {return "A Function";},
    "B": function() {return "B Function";},
    "C": function() {return "C Function";}
}

function doWork()
{
    var funcToRun;
    
    new Promise(function(resolve,reject) {
        var answer = prompt('Starting.  Please pick a letter: A,B,C');
        if(myNamespace[answer] === undefined)
        {
            alert("Invalid choice!");
            reject("Invalid choice of: " + answer);
        }
        else
        {
            resolve(answer);
        }
    })
    .then(function(response) {
        funcToRun = myNamespace[response]();})
    .then(function(){
        document.getElementById('result').innerHTML = funcToRun;})
    .then(function(){
        if(prompt("Run Again? (YES/NO)")==="YES")
        {
            doWork();
        }
    });
}

doWork();

<div id="result"></div>

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