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JavaScript : Create an object composed of the properties the given function returns truthy for

JavaScript fundamental (ES6 Syntax): Exercise-97 with Solution

Write a JavaScript program to create an object composed of the properties the given function returns truthy for. The function is invoked with two arguments: (value, key).

  • Use Object.keys(obj) and Array.prototype.filter()to remove the keys for which fn returns a falsy value.
  • Use Array.prototype.reduce() to convert the filtered keys back to an object with the corresponding key-value pairs.
  • The callback function is invoked with two arguments: (value, key).

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const pickBy = (obj, fn) =>
  Object.keys(obj)
    .filter(k => fn(obj[k], k))
    .reduce((acc, key) => ((acc[key] = obj[key]), acc), {});
console.log(pickBy({ a: 1, b: '2', c: 3 }, x => typeof x === 'number'));

Sample Output:

{"a":1,"c":3}

Flowchart:

flowchart: Create an object composed of the properties the given function returns truthy for

Live Demo:

See the Pen javascript-basic-exercise-97-1 by w3resource (@w3resource) on CodePen.


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Next: Write a JavaScript program to filter an array of objects based on a condition while also filtering out unspecified keys.

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JavaScript: Tips of the Day

Chunks an array into n smaller arrays

Example:

const tips_chunkIntoN = (arr, n) => {
  const size = Math.ceil(arr.length / n);
  return Array.from({ length: n }, (v, i) =>
    arr.slice(i * size, i * size + size)
  );
}
console.log(tips_chunkIntoN([1, 2, 3, 4, 5, 6, 7,8], 4)); 

Output:

[[1,2],[3,4],[5,6],[7,8]]