React: How to access array in an object?

Question

Bit of a rookie question & late in the day, but how do I access an array in an object? I am getting undefined & TypeError: Cannot read property 'length' of undefined. I can get the object data (Id, ElemId, etc) fine.

...
this.state = {
   yfinder: [],
   ...
}

...then api call...
this.setState({
  finder: res.Finder,
  ...
})

JSON:

"Finder": {
    "Id": "23216245567u4",
    "ElemId": "finder",
    "Title": "Your Finder",
    "Description": "This is a description",
    "ResultsTitle": "What program or service are you looking for?",
    "CategoryTitle": "Great! Select a category to continue..",
    "Results": [
       {
         ...
       }
       {
         ...
       }
    ]
}
let finder = this.state.finder;
console.log(finder.Results);

for (var i = 0; i < finder.Results.length; i++) {
  console.log(finder.Results[i]); 
}

Maybe try let finder = this.state.Finder

ferhen
– ferhen

2020-03-17 05:55:22 +00:00
Commented Mar 17, 2020 at 5:55 — ferhen
– ferhen, Commented Mar 17, 2020 at 5:55

Atin Singh · Accepted Answer · 2020-03-17 05:59:53Z

2

That's because initially your finder object doesn't have Results array. Try this and see if this works.

let finder = this.state.finder;
console.log(finder.Results);
const resultsLength = finder.Results ? finder.Results.length : null;

for (var i = 0; i < resultsLength; i++) {
  console.log(finder.Results[i]); 
}

answered Mar 17, 2020 at 5:59

Atin Singh

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Comments

Sanu Kumar · Accepted Answer · 2020-03-17 06:41:28Z

0

You can simply use . operator to access the key of object and use map to traverse the items of array inside the object.

e.g : 
let obj = {
  topic: "accessing array in an object",
  fruits: [
    { name: "banana", price: 30 },
    { name: "apple", price: 50 }
  ]
};

obj.fruits.map(fruit => console.log(fruit.name));

I hope, it helps you.

answered Mar 17, 2020 at 6:41

Sanu Kumar

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