Promises: Repeat operation until it succeeds?

Question

I want to perform an operation repeatedly, with an increasing timeout between each operation, until it succeeds or a certain amount of time elapses. How do I structure this

Answer 1

Here's an example of how I'd approach this, with some helper functions. Note, the 'maxTimeout' is the more complicated part because you have to race two states.

// Helper delay function to wait a specific amount of time.
function delay(time){
    return new Promise(function(resolve){
        setTimeout(resolve, time);
    });
}

// A function to just keep retrying forever.
function runFunctionWithRetries(func, initialTimeout, increment){
    return func().catch(function(err){
        return delay(initialTimeout).then(function(){
            return runFunctionWithRetries(
                    func, initialTimeout + increment, increment);
        });
    });
}

// Helper to retry a function, with incrementing and a max timeout.
function runFunctionWithRetriesAndMaxTimeout(
        func, initialTimeout, increment, maxTimeout){

    var overallTimeout = delay(maxTimeout).then(function(){
        // Reset the function so that it will succeed and no 
        // longer keep retrying.
        func = function(){ return Promise.resolve() };
        throw new Error('Function hit the maximum timeout');
    });

    // Keep trying to execute 'func' forever.
    var operation = runFunctionWithRetries(function(){
        return func();
    }, initialTimeout, increment);

    // Wait for either the retries to succeed, or the timeout to be hit.
    return Promise.race([operation, overallTimeout]);
}

Then to use these helpers, you'd do something like this:

// Your function that creates a promise for your task.
function doSomething(){
    return new Promise(...);
}

runFunctionWithRetriesAndMaxTimeout(function(){
    return doSomething();
}, 1000 /* start at 1s per try */, 500 /* inc by .5s */, 30000 /* max 30s */);