AngularJS $q service response in sequence with exception handling

Question

I have a function which gives me response in sequence for asynchronous call using promises for a for loop but loop breaks when i got a exception from code, but i want to continue my loop even after a exception throw from function.

my async function is

function asyncFun(a) { 
    var q = $q.defer(); 
    setTimeout(function(){
        if(a == 4) throw new Error('custom error'); 
        q.resolve(a);
    }, 1000); 
    return q.promise; 
}

and chain function is

function getData() {
    var chain = $q.when();
    for (var i = 0; i < 10; i++) {
        (function(i) {
            chain = chain.then(function() {
                return asyncFun(i).then(function(res) {
                    console.log(res);
                }).catch(function(ex) {
                    throw ex;
                });
            }).catch(function(ex) { throw ex });
        })(i);
    };
    return chain
}

and when i call getData(); it stop the loop after throw error on i = 4 but i want to continue the for loop for all 10 entry.

Any help will be appreciated.

How will you hangle the error? There is no way that one of your promise is rejected while you're continuing to perform the loop. Maybe you should treat that error as a special value and resolve it as you resolve normal value. — Wing-On Yuen, Jul 27 '17 at 20:24
My `asyncFun` is predefined with throw error in some condition, that why i need changes in `getData` for completing the loop. — Gaurav Kumar Singh, Jul 28 '17 at 07:35
why did vote down this question without understanding the problem — Gaurav Kumar Singh, Jul 28 '17 at 07:36
I did not vote down this question. Maybe it's another guy... — Wing-On Yuen, Jul 28 '17 at 08:03

score 0 · Answer 1 · answered Jul 28 '17 at 08:41

As I said in comment, the errors may be treated as special values so you can perform special behaviours after the chain promises.

Try this code:

function getData() {
    var chain = $q.when();
    for (var i = 0; i < 10; i++) {
        (function(i) {
            chain = chain.then(function() {
                return asyncFun(i).then(function(res) {
                    console.log(res)
                }).catch(function(ex) {
                    console.log(ex); // do not throw error but handle the error
                });
            }).catch(function(ex) { throw ex });
        })(i);
    };
    return chain
}

AngularJS $q service response in sequence with exception handling

1 Answers1