How to pass value of a variable as a key or parameter to a variable inside curly brackets?

Question

How to pass a variable to an array key where the array is an another variable that is inside a curly bracket. In the following code I'm trying to push values from source array if the value is greater than 50.

render(){
  var source_arr = [35,45,50,60,20];
  var dest_array = [];
  for(var x=0; x<source_arr.length; x++){
    if(source_array[x]>50){
      dest_array.push({source_array[x]});
    }
  }
  return(
    <div>
    </div>
  )
}

Here I'm not able to pass the value of variable 'x' as the array key inside the for loop.

It's not at all clear what you want to do here. Please show us examples of inputs and the results you expect. For one thing, the above doesn't make a lot of sense, since `source_arr` is empty and you'll never go into the loop. — T.J. Crowder, Sep 26 '19 at 07:48
I don't think you should use push as that mutates dest_array, Maybe do `new_dest=dest_array.concat(source_array.filter(item=>condition)` — HMR, Sep 26 '19 at 07:49
@HMR - It's a local, mutating it is perfectly fine. No reason to constantly create new arrays here. But depending on what the OP wants, `filter` might be the way to go... — T.J. Crowder, Sep 26 '19 at 07:52
@LalasM - That doesn't address my comment above. What result do you want? — T.J. Crowder, Sep 26 '19 at 08:17

score 0 · Answer 1 · answered Sep 26 '19 at 07:48

0

You need to make use of [] to define keys

render(){
  var source_arr = [];
  var dest_array = [];
  for(var x=0; x<source_arr.length; x++){
    if(a condition){
      dest_array.push({[source_array[x]]:source_array[x] });
    }
  }
  return(
    <div>
    </div>
  )
}

answered Sep 26 '19 at 07:48

Shubham Khatri

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@LalasM "some syntax error" is useless. ***What*** syntax error? The above is valid ES2015+. If this is what you're trying to do, and you need to do it in ES5, see [this question's answers](https://stackoverflow.com/questions/695050/add-a-property-to-a-javascript-object-using-a-variable-as-the-name). – T.J. Crowder Sep 26 '19 at 08:16
@T.J.Crowder syntax error is rectified. thanks Shubham Khatri syntax error was a typo – Lalas M Sep 26 '19 at 08:17
@LalasM - I don't know what you mean. The answer above has not been edited since your comment was made. – T.J. Crowder Sep 26 '19 at 08:18

score 0 · Answer 2 · answered Sep 26 '19 at 07:57

Looks like you want to map all items in source array to objects if a condition is true or false:

const source_arr = [
  {name:'hi',age:22},
  {name:'bye',age:88},
];
const dest_arr = source_arr
  .map(
    //map item to object or false
    item => item.age<40 && { [item.name]: item.age }
  )
  .filter(x => x); //remove all false items
console.log(dest_arr);

You can combine the map and filter in one reduce:

const source_arr = [
  { name: 'hi', age: 22 },
  { name: 'bye', age: 88 },
];
const dest_arr = source_arr.reduce(
  (result, item) =>
    //add object if condition is true
    item.age < 40
      ? result.concat({ [item.name]: item.age })
      : result,
  []
);
console.log(dest_arr);

How to pass value of a variable as a key or parameter to a variable inside curly brackets?

2 Answers2