JavaScript Creating array in object and push data to the array

Question

I'm new to programming. I'm trying React and have function addComment which is executed when a user adds a comment to news.I need to create in this moment a property comments (array) and assign or push to this array inputCommentValue value. But right now I only rewrite 0 element of the array and can't add a new element. Can you please tell me where to put push method? Thank you!

var ARTICLES = [{
  title: "sit amet erat",
  text: "nam dui proin leo odio porttitor id consequat in consequat ut nulla sed accumsan"

}, {
  title: "pulvinar sed",
  text: "velit id pretium iaculis diam erat fermentum justo nec condimentum"
}]



addComment(index, inputCommentValue){
ARTICLES = [...ARTICLES], ARTICLES[index].comments=[inputCommentValue];
this.setState({ARTICLES:ARTICLES});
}

Yes, ARTICLES is my state. It is updated properly. My problem is that I can't understand how to define (create) array and use method concat on it in the same time. I tried something like this: ARTICLES = [...ARTICLES], ARTICLES[index].comments=[].concat(inputCommentValue); But it works only for first element, next time (when user adds next comment) it rewrites array because of this comments=[] — Rinat Rezyapov
– Rinat Rezyapov, Commented Jul 11, 2016 at 12:21

Divyanth Jayaraj · Accepted Answer · 2016-07-11 13:58:47Z

2

Let's say you have an object like this.

   foo : {
       bar : "x"
    }

To create an array, simply initialize it to an empty array.

foo.newArray = []

If you console.log(foo), you will now see this

foo : {
   bar : "x",
   newArray : []
 }

This means your foo object has an empty array called newArray. You can add elements to it using the push() method.

Push a variable like this foo.newArray.push(myVariable); Push a string like this foo.newArray.push("myString"); Push an object like this

 foo.newArray.push({
    "bar2" : "val2"
 });

For more information on arrays check W3schools

In your particular case, just do ARTICLES.push({})

answered Jul 11, 2016 at 13:58

Divyanth Jayaraj

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Rinat Rezyapov Over a year ago

Divyanth Jayaraj, thank you for this explanation! Now it is clearer for me!

Kokovin Vladislav · Accepted Answer · 2016-07-11 12:24:29Z

1

assuming that data exist in component's state , then handler will look something like that

addComment(index, inputCommentValue){
    // copy array , for not mutate state
    let ARTICLES = [...this.state.ARTICLES];
    // check if comments not exist
    if(!ARTICLES[index].comments) ARTICLES[index].comments=[];
    // add new comment to array
    ARTICLES[index].comments.push(inputCommentValue);
    // update component with new articles
    this.setState({ARTICLES:ARTICLES});
}

answered Jul 11, 2016 at 12:24

Kokovin Vladislav

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