typescript - Javascript Promise.all confusion -

i using javascript/typescript in order format password value on collection of personmodel objects. executing promise on each element in collection.

i using promise.all allow promises complete, , want return formatted collection.

however, error @ build time.

personservice.ts

private decryptpersons(persons: personmodel[]): promise<personmodel[]> {     return new promise<personmodel[]>(resolve => {         let promises: array<promise<string>> = [];         let decryptedpersons: personmodel[] = [];         (let i: number = 0; < persons.length; i++) {             let ciphertext: string = persons[i].password;             promises.push(this.decrypt(ciphertext).then((password: string) => {  // <== line 357                 persons[i].password = password;                 decryptedpersons.push(persons[i]);             }));         }         promise.all(promises).then(() => {             resolve(decryptedpersons);         });     }); }  private decrypt(value: string): promise<string> {     return new promise<string>(resolve => {         this.encrypter.decrypt(value).then((result: string) => {             resolve(result);         });     }); } 

error

error in ./app/pages/service/personservice.ts (357,31): error ts2345: argument of type 'promise<void>' not assignable parameter of type 'promise<string>'.   type 'void' not assignable type 'string'. 

i no expert javascript, structure may me incorrect. if can advise, appreciate it.

you're trying push following promises array:

this.decrypt(ciphertext).then((password: string) => {  // <== line 357     persons[i].password = password;     decryptedpersons.push(persons[i]); }) 

but function here doesn't return anything, going evaluate promise<void>.

you're abusing "explicit promise construction antipattern" in several places here.

give try:

private decryptpersons(persons: personmodel[]): promise<personmodel[]> {     return promise.all(persons.map(person =>         this.decrypt(person.password)             .then(password => {                 person.password = password;                 return person;             });     )); }  private decrypt(value: string): promise<string> {     return this.encrypter.decrypt(value); }