Angular Promise trying Wrapper

Question

Sometimes I need to repeat an execution of rejected promises several times, for example, to fetch some data over internet. There is a wrapper, which accepts Promise and tryCount:

function tryPromise(f, tryCount) {
 return f().then(null, function(v) {
 tryCount--;
 if (tryCount > 0) {
 return $q.reject(v);
 }
 return tryPromise(f, tryCount);
 });
}

Is there some hidden troubles?

• Sergio: What is $q in return $q.reject(v);?
• Vladimir Gamalyan: @Sergio Angular's Promise docs.angularjs.org/api/ng/service/$q
• Sergio: if tryCount is <= 0 that code will enter a loop and kill your browser if there is no waiting moment in f.. What numbers to you give tryCount when you invoque that function? will it ever be <=0?
• Vladimir Gamalyan: @Sergio you are right, will be better to place additional conditional for that case.

Answer 1

Well, first of all you aren't trying a promise. What you're really doing is trying out a function that returns a promise. So the name is already misleading. Try something better.

Next, f and v doesn't really tell me anything. Only when I read through the code did I realize f was the function to try out and v is supposed to be a value. Additionally, even if you name v a value, it's still not correct. Most reject handlers often pass an error object.

Code that requires one to actually read to understand is a bad practice. In this case it's negligible due to the size of the function. But if you're in larger codebases, it's a nightmare to maintain. Name your functions and variables meaningfully.

Lastly, your function doesn't allow for function arguments. It would be nice to at least accept argument 3 onwards as the arguments, or accept an array that would be the arguments.

My take on it would be:

function tryPromiseFunction(functionToTry, retries, ...args){
 return functionToTry(...args).then(null, error => {
 return retries > 0 ? tryPromiseFunction(functionToTry, retries - 1, ...args)
 : Promise.reject(error);
 });
}

• Vladimir Gamalyan: Looks good, many thanks. Not sure, should we compare retries with > 1instead > 0 ?