Specify properties for objects inside an array of objects

Question

I have an interface that looks like this:

    export interface Stats {

    lastFiveResults: Object[];

}

The array of objects looks this this:

(5) [{…}, {…}, {…}, {…}, {…}]
0: {idresults: 500, gold: 567740, mana: 305370, xp: 1800}
1: {idresults: 501, gold: 492381, mana: 602707, xp: 1450}
2: {idresults: 502, gold: 241012, mana: 303954, xp: 810}
3: {idresults: 503, gold: 415778, mana: 261254, xp: 810}
4: {idresults: 504, gold: 327266, mana: 427803, xp: 0}

And when I try and access it like this

data.lastFiveMatches[0].gold

I get Property gold does not exist on type object

So my question is how do I specify these properties?

It seems that error appears when the lastFiveMatches.length === 0. — Amir Christian
– Amir Christian, Commented Oct 16, 2019 at 7:11
He would get "Cannot read property of undefined" if length === 0. Problem is that he doesn't have typed lastFiveResults property. — zhuber
– zhuber, Commented Oct 16, 2019 at 7:16

Yosvel Quintero · Accepted Answer · 2019-10-16 07:07:59Z

1

You should create the interfaces Item and ResultItem:

export interface ResultItem {
  idresults: number;
  gold: number; 
  mana: number;
  xp: number;
}

export interface Stats {
  lastFiveResults: ResultItem[];
}

... and then:

data.lastFiveMatches[0].gold;

answered Oct 16, 2019 at 7:07

Yosvel Quintero

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Comments

Nithya Rajan · Accepted Answer · 2019-10-16 07:02:13Z

0

You can define another interface to specify the type of properties in your object.

interface myObject {
  idresults: number,
  gold: number,
  mana: number,
  xp: number
}

export interface Stats {

    lastFiveResults: myObject[];

}

answered Oct 16, 2019 at 7:02

Nithya Rajan

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Comments

Shikha · Accepted Answer · 2019-10-16 07:02:45Z

0

export class Stats {
    lastFiveResults: Object[]=[{…}, {…}, {…}, {…}, {…}]
}

in your ts file:

data= new Stats();
console.log(data.lastFiveMatches[0].gold)

answered Oct 16, 2019 at 7:02

Shikha

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Comments

zhuber · Accepted Answer · 2019-10-16 07:05:18Z

0

You can define interface or type for your object within the list

export interface Stats {
    lastFiveResults: MyObject[];
}

export interface MyObject {
  idresults: number
  gold: number
  mana: number
  xp: number
}

Please see this playground.

answered Oct 16, 2019 at 7:05

zhuber

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Comments

Amir Christian · Accepted Answer · 2019-10-16 07:13:53Z

0

Try this:

if (data.lastFiveMatches && data.lastFiveMatches.length > 0) {    
   const something = data.lastFiveMatches[0].gold || 0;
}

edited Oct 16, 2019 at 7:13

answered Oct 16, 2019 at 7:07

Amir Christian

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Comments

StepUp · Accepted Answer · 2019-10-16 07:24:05Z

0

You can declare like this:

export interface Stat {
    idresults: number, 
    gold:  number, 
    mana:  number, 
    xp:  number
}

and to initialize:

yourStats: Stat[]= [];

fooMethod() {    
    for (let i = 0; i<10; i++) {
        console.log('1');
        this.yourStats.push({idresults: i, gold: i, mana: i, xp: i})
    } 
    console.log(`Your stats is`, this.yourStats);    
}

edited Oct 16, 2019 at 7:24

answered Oct 16, 2019 at 7:02

StepUp

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