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

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

Object from Truthy Function Keys

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
// Define the 'pickBy' function to pick key-value pairs from an object based on a filtering function.
const pickBy = (obj, fn) =>
  // Filter the keys of the object based on the filtering function 'fn', then reduce them to build a new object.
  Object.keys(obj)
    .filter(k => fn(obj[k], k)) // Filter keys based on the filtering function.
    .reduce((acc, key) => ((acc[key] = obj[key]), acc), {}); // Build a new object containing the filtered key-value pairs.

// Test the 'pickBy' function with an object and a filtering function.
console.log(pickBy({ a: 1, b: '2', c: 3 }, x => typeof x === 'number')); // Output: { a: 1, c: 3 }

Output:

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

Flowchart:

Live Demo:

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

For more Practice: Solve these Related Problems:

• Write a JavaScript program that creates an object containing only the key-value pairs for which a provided function returns truthy for the key.
• Write a JavaScript function that filters an object’s properties based on a callback applied to each key and returns the filtered object.
• Write a JavaScript program that iterates over an object and constructs a new object with properties passing a truthy test.

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