I want to initialize an interface in TypeScript.

export interface TestGroup {
  "id": number;
  "type": TestType;
  "interval"?: number;
}


import {TestGroup} from "../../gen/api";
public functionConfig: TestGroup;
.
.
.
this.functionConfig.id = testGroup.functionTestConfig;

I get this error:

TypeError: Cannot set property 'id' of undefined

Could you please help me?

I want to initialize an interface in TypeScript.

export interface TestGroup {
  "id": number;
  "type": TestType;
  "interval"?: number;
}


import {TestGroup} from "../../gen/api";
public functionConfig: TestGroup;
.
.
.
this.functionConfig.id = testGroup.functionTestConfig;

I get this error:

TypeError: Cannot set property 'id' of undefined

Could you please help me?

• javascript
• typescript
• undefined

• you need to initialize functionConfig to some value, right now it is undefiend and you end up doing undefined.id which is not valid javascript. – toskv Commented Jun 19, 2017 at 13:36
• What is this? Where was this.functionConfig set? Are we supposed to guess? – user47589 Commented Jun 19, 2017 at 13:36
• Well you declare functionConfig but you don't assign it any value, therefore it is undefined. If you do something like this.functionConfig = { test : "value" } or even just this.functionConfig = { } it will be defined, so afterwards, you can do this.functionConfig.id = "whatever" – Jeremy Thille Commented Jun 19, 2017 at 13:38

2 Answers 2

Your functionConfig has a type but it is actually undefined. So you need to initialize it:

public functionConfig: TestGroup = {id: 0, type: 'YourTestTypeHere'};

or your default values for it

Comment

var activateOnWeekDay: Array<boolean> = [];

You can fix it by initializing an empty object {}.

export interface TestGroup {
  id: number;
  type: TestType;
  interval?: number;
}


import {TestGroup} from "../../gen/api";
public functionConfig: TestGroup = {};        <=====Assign empty object
.
.
.
this.functionConfig.id = testGroup.functionTestConfig;