Angular 2 TypeScript how to find element in Array

问题

I have a Component and a Service:

Component:

export class WebUserProfileViewComponent {
    persons: Person [];
    personId: number;
    constructor( params: RouteParams, private personService: PersonService) {
          
        
           this.personId = params.get('id');
           this.persons =  this. personService.getPersons();
           console.log(this.personId);  
        }
}

Service:

@Injectable()
export class PersonService {
      getPersons(){
        var persons: Person[] = [
            {id: 1, firstName:'Hans', lastName:'Mustermann', email: 'mustermann@test.com', company:'Test', country:'DE'},
            {id: 2, firstName:'Muster', lastName:'Mustermann', email: 'mustermann@test.com', company:'test', country:'DE'},
            {id:3, firstName:'Thomas', lastName:'Mustermann', email: 'mustermannt@tesrt.com', company:'test', country:'DE'}
        ];
          
        return persons;
      }
}

I want to get the Person Item with the Id ('personID'). The personID i get from Routeparam. For that I need the foreach loop? But I haven´t found a solution for this.

回答1:

You need to use method Array.filter:

this.persons =  this.personService.getPersons().filter(x => x.id == this.personId)[0];

or Array.find

this.persons =  this.personService.getPersons().find(x => x.id == this.personId);

回答2:

Assume I have below array:

Skins[
    {Id: 1, Name: "oily skin"}, 
    {Id: 2, Name: "dry skin"}
];

If we want to get item with Id = 1 and Name = "oily skin", We'll try as below:

var skinName = skins.find(x=>x.Id == "1").Name;

The result will return the skinName is "Oily skin".

Please take a try, Thanks and best regard!

回答3:

Transform the data structure to a map if you frequently use this search

mapPersons: Map<number, Person>;

// prepare the map - call once or when person array change
populateMap() : void {
    this.mapPersons = new Map();
    for (let o of this.personService.getPersons()) this.mapPersons.set(o.id, o);
}
getPerson(id: number) : Person {
    return this.mapPersons.get(id);
}

回答4:

A neat option not yet mentioned is to use combine .find with arrow functions and destructuring. Take this example from MDN.

const inventory = [
  {name: 'apples', quantity: 2},
  {name: 'bananas', quantity: 0},
  {name: 'cherries', quantity: 5}
];

const result = inventory.find( ({ name }) => name === 'cherries' );

console.log(result) // { name: 'cherries', quantity: 5 }

回答5:

from TypeScript you can use native JS array filter() method:

let filteredElements=array.filter(element => element.field == filterValue);

it returns an array with only matching elements from the original array (0, 1 or more)

Reference: https://developer.mozilla.org/it/docs/Web/JavaScript/Reference/Global_Objects/Array/filter

回答6:

Use this code in your service:

return this.getReports(accessToken)
        .then(reports => reports.filter(report => report.id === id)[0]);

回答7:

Try this

          let val = this.SurveysList.filter(xi => {
        if (xi.id == parseInt(this.apiId ? '0' : this.apiId))
          return xi.Description;
      })

      console.log('Description : ', val );

来源：https://stackoverflow.com/questions/37969984/angular-2-typescript-how-to-find-element-in-array

标签

angular

typescript

angular2-services