I am writing a SPA with typescript using breeze and knockout.
What I want to do is to create a launch manager, which can perform the neccessary steps required to even start the site (e.g. read configuration json, download odata metadata, initialize breeze metadata store and so on).
I've created the following to represent each step in the launch sequence:
export enum LauncherProgressStatus {
Ready,
InProgress,
Success,
Failed,
Aborted
}
export class LauncherProgressItem {
public status: KnockoutObservable<LauncherProgressStatus> = ko.observable<LauncherProgressStatus>();
public description: KnockoutObservable<String> = ko.observable<String>();
public statusText: KnockoutComputedFunctions<String> = ko.computed<String>(() => {
return LauncherProgressItem.getStatusText(this.status());
});
public start() {
this.action(this);
}
constructor(descriptionText: String,
public action: (arg: LauncherProgressItem) => Boolean) {
this.status(LauncherProgressStatus.InProgress);
this.description(descriptionText);
}
public static getStatusText(status: LauncherProgressStatus) : String {
switch (status) {
case LauncherProgressStatus.Ready:
return "Ready";
case LauncherProgressStatus.InProgress:
return "In progress";
case LauncherProgressStatus.Success:
return "Success";
case LauncherProgressStatus.Aborted:
return "Aborted";
default:
return "Failed";
}
}
}
TL;DR I create each step like this in code:
var item1 = new launcher.LauncherProgressItem("Loading configuration...", (item: LauncherProgressItem) => {
cfgMgr.setConfigurationFromFile("config.json?bust=" + (new Date()).getTime());
return true;
});
Now the problem: I want to utilize this to create a promise chain using Q. I can do this manually, i.e.
q.fcall(() => item1.action(item1))
.then(() => item2.action(item2))
.fail((r) => { console.log("Many whelps, HANDLE IT!") });
But I want to create some kind of manager object that doesnt really know how many steps is required. It will just be responsible for building an array of promises and execute them in sequence, whilst being able to detect errors (in the fail promise presumably) and abort the sequence.
The manager will have some kind of collection containing the LauncherProgressItem steps. Then I'm looking to build a chain of promises based on the content of that collection.
I've been looking at this for a while now but can't really seem to get my head around how to do this with Q. I've seen some examples etc but I don't really understand how it works.
Anyone got any suggestions on how to achieve this?
Update: I'll try to clarify what I am trying to achieve: My LauncherProgressItem wraps a lambda function and some state information which I bind to my view. This is why I am using these, but this is kind of irrelevant to what I'm actually struggling with.
So lets assume I have a class which contains an array of lambdas. This class has a method which will run all these lambas in sequence using Q, aborting on error. Exactly what I would achieve with the following code:
Q.fcall(doSomething).then(doSomethingElse).fail(reportError);
However, in this case doSomething and doSomethingElseresides in an array of functions, rather than a fixed number of steps. This is because I want it to be reusable, i.e. being able to run in multiple scenarios depending on the task at hand. So I want to avoid hard-coding the chain of functions to run.
