Typescript - Index signature is missing in type - Contextual Typing

Question

I have the following class and a subclass

export class FlightInfoModel {
    carrierName?: string;
    originCode?: string;
    destCode?: string;
    flightDetails: FlightSegmentEntity[];

    constructor() {
        this.carrierName = "";
        this.originCode = "";
        this.destCode = "";
        this.flightDetails = new Array<FlightSegmentEntity>();
    }
}

export class FlightSegmentEntity {
  CarrierCode: string;
  FlightNo: string;
  Aircraft: string;

  OriginCode: string;
  DestinationCode: string;

  DepartureDate: string;
  ArrivalDate: string;

  FlightDuration: number;
  StopOverDuration: string;

  constructor() {
    this.CarrierCode = "";
    this.FlightNo = "";
    this.Aircraft = "";
    this.OriginCode = "";
    this.DestinationCode = "";
    this.DepartureDate = "";
    this.ArrivalDate = "";
    this.FlightDuration = -1;
    this.StopOverDuration = "";
  }

I am using Typescript and UnderscoreJS to write the following function. flight is the FlightInfoModel object and flightDetails is the FlightSegmentEntity[]

_.reduce(flight.flightDetails,
function(memo, seg){ return memo + seg.FlightDuration + seg.StopOverDuration; },
0)

The underscore function accepts an array collection but I keep getting the following error

error TS2345: Argument of type 'FlightSegmentEntity[]' is not assignable to parameter of type 'Dictionary<{}>'. Index signature is missing in type 'FlightSegmentEntity[]'.

I have read a lot about the contextual typing that Typescript requires and tried doing that but to no avail. BTW I am using Typescript 2.3.4

https://stackoverflow.com/questions/37006008/typescript-index-signature-is-missing-in-type — lohiarahul, Jun 19 '17 at 13:11

Remo H. Jansen · Answer 1 · 2017-06-19T14:23:41.860

0

The code that you pasted is missing parseInt(seg.StopOverDuration):

const total = _.reduce(flight.flightDetails, (t, seg) => {
    return t + (seg.FlightDuration + parseInt(seg.StopOverDuration));
}, 0);

But the error is about dictionaries:

Argument of type 'FlightSegmentEntity[]' is not assignable to parameter of type 'Dictionary<{}>'.

You don't have a Dictionary<T> in the pasted code so my guess is that you need to share more details.

Update

I tested the following and works without errors:

import * as _ from "underscore";

class FlightInfoModel {

    public carrierName: string;
    public originCode: string;
    public destCode: string;
    public flightDetails: FlightSegmentEntity[];

    public constructor() {
        this.carrierName = "";
        this.originCode = "";
        this.destCode = "";
        this.flightDetails = new Array<FlightSegmentEntity>();
    }
}

class FlightSegmentEntity {
  public CarrierCode: string;
  public FlightNo: string;
  public Aircraft: string;

  public OriginCode: string;
  public DestinationCode: string;

  public DepartureDate: string;
  public ArrivalDate: string;

  public FlightDuration: number;
  public StopOverDuration: string;

  public constructor() {
    this.CarrierCode = "";
    this.FlightNo = "";
    this.Aircraft = "";
    this.OriginCode = "";
    this.DestinationCode = "";
    this.DepartureDate = "";
    this.ArrivalDate = "";
    this.FlightDuration = -1;
    this.StopOverDuration = "";
  }
}

const flight = new FlightInfoModel();

const result = _.reduce(flight.flightDetails, (memo, seg) => {
        return memo + seg.FlightDuration + parseInt(seg.StopOverDuration);
    },
    0
);

alert(result);

edited Jun 19 '17 at 14:23

answered Jun 19 '17 at 12:31

Remo H. Jansen

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http://underscorejs.org/#reduce You could see that this function accepts an array. Doesn't need a dictionary. – lohiarahul Jun 19 '17 at 12:46
Where have you defined `Dictionary`? – Remo H. Jansen Jun 19 '17 at 12:50
var sum = _.reduce([1, 2, 3], function(memo, num){ return memo + num; }, 0); This is the example on the website. They havent passed a dictionary as the first argument either. – lohiarahul Jun 19 '17 at 12:52
https://stackoverflow.com/questions/37006008/typescript-index-signature-is-missing-in-type – lohiarahul Jun 19 '17 at 13:11
These links might give a clearer idea on what lines the problem seems to be – lohiarahul Jun 19 '17 at 13:15
You don't need to pass a Dictionary you need to pass an Array (as you are doing) but the error is mentioning a Dictionary. Are you sure that you error is in the call to `_.reduce` and not somewhere else? – Remo H. Jansen Jun 19 '17 at 13:59
Yes. 100% sure. – lohiarahul Jun 19 '17 at 14:08
I have added the entire code snippet that I used to test it. I don't get any errors so I don't think I can help you :( – Remo H. Jansen Jun 19 '17 at 14:24
props.flightInfo.map((flight: FlightInfoModel, i: any) =>{//underscorejs.reduce used here} – lohiarahul Jun 19 '17 at 14:51
I guess because you instantiated with the new keyword the problem didn't occur for you – lohiarahul Jun 19 '17 at 14:52
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/147085/discussion-between-lohiarahul-and-remo-h-jansen). – lohiarahul Jun 19 '17 at 14:52

Typescript - Index signature is missing in type - Contextual Typing

1 Answers1

Update