CODEWITHSUNDEEP
javascripteventsasynchronousasync-await
user2671505
user2671505

Reputation: 55

How to use Promise to wait for event inside function finish then call this function again?

I use dojo in Javascript and write a global function that has async function inside its. I want to call these function twice in a row ,but I want the first call finish before call the second.

I don't have source code right now but the structure is look like these.

initDataStore("store1");
initDataStore("store2");

 initDataStore : function(storeName){
         var request = openDB(storeName);
         request.onUpgradeneed(function(){
             //set some global value without return value
         });
         request.onSuccess(function(){
             //set some global value without return value
         });
    }

I just try to use promise like these but I not sure if its work or not.

var p = Promise.resolve(initDataStore("store1"));
  p.then(function(){initDataStore("store2")});

     initDataStore : function(storeName){
             var request = openDB(storeName);
             request.onUpgradeneed(function(){
                 //set some global value without return value
               return new Promise(function (resolve, reject){resolve("success"});
             });
             request.onSuccess(function(){
                 //set some global value without return value
               return new Promise(function (resolve, reject){resolve("success"});
             });
        }

How to reslove these problem in the correct way?

PS. I don't want any return value ,I just want initDataStore("store2") to call after onUpgradeneed or onSuccess of initDataStore("store1") finish.

Upvotes: 3

Views: 3335

Answers (1)

Johannes Lemonde
Johannes Lemonde

Reputation: 204

Nope, it won't work. You actually let the upgradeneed and success event function return a promise, but you actually don't let initDataStore return any thing...

Promises work this way : 

function init(someParam){
   return new Promise(function(resolve, reject){
      // do something here
      // and call either resolve(someValue) or reject(someValue)
   });
}
init("aaa").then(function(val){/*success*/}, function(err){/*error*/});

Which should give us following:

function initDataStore(storeName){
   return new Promise(function(resolve, reject){
         var request = openDB(storeName);
         request.onUpgradeneed(function(){
             reject("Upgrade needed !");
         });
         request.onSuccess(function(){
             resolve("OK !");
         });
   });
}
initDataStore("store1").then(function(val){
   // val contains "OK !"
   initDataStore("store2").catch(function(err){/*second one did not work*/});
}, function(err){
   // first one did not work
   // err contains "Upgrade needed !"
});

Upvotes: 2

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