Why am I receiving an undefined value?

I am currently engaged in Angular4 development and have encountered an issue that I cannot seem to resolve. The problem arises when I attempt to store a value on the service provider and retrieve it from a component. Below is a snippet of my code:

Service Provider:

key:any;
constructor(){}
    storeKeysAppPreferences(res){
            this.appPreferences.clearAll();
            console.log("storeKeysAppPreferences",res);
            this.appPreferences.store('key1',JSON.stringify(res));
        }

        fetchKeysAppPreferences(){
          this.appPreferences.fetch("key1").then(
            (res) => {
                this.key=(JSON.parse(res));
              }
           );
        }

Upon calling console.log()

fetchKeysAppPreferences(){
  this.appPreferences.fetch("key1").then(
    (res) => {
        this.key.push(JSON.parse(res));
        console.log(this.key); //is definded
      }
   );
   console.log(this.key); // undefined
}

Surprisingly, the value of key turns out to be undefined. Can anyone shed some light on why this might be happening?

Answer №1

Since this is an asynchronous operation, you will need to structure your code as shown below:

Please Note: The following demonstrates the concept only. Be sure to arrange the methods according to your specific use case.

constructor(){}
    storeAppPreferencesKeys(res){
        this.appPreferences.clearAll();
        console.log("Storing App Preferences Keys", res);
        
        this.appPreferences.store('key1', JSON.stringify(res)).then(()=>{//handle success
            fetchAppPreferencesKeys(){
                this.appPreferences.fetch("key1").then(
                    (res) => {
                        this.key = JSON.parse(res);
                    }
                );
            }
        });
    }

Answer №2

It is imperative to place

console.log(this.key); // undefined
within the callback function as the second console.log() gets executed prior to the response being fully prepared.

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