JavaScript: Get the first key that satisfies the provided testing function

JavaScript fundamental (ES6 Syntax): Exercise-236 with Solution

First Key Satisfying Condition

Write a JavaScript program to get the first key that satisfies the provided testing function. Otherwise return undefined.

• Use Object.keys(obj) to get all the properties of the object, Array.prototype.find() to test each key-value pair using fn.
• The callback receives three arguments - the value, the key and the object.

Sample Solution:

JavaScript Code:

// Define a function 'findKey' to find the first key in an object that satisfies a provided testing function
const findKey = (obj, fn) =>
  Object.keys(obj).find(key => fn(obj[key], key, obj)); // Find the first key that satisfies the condition

// Test the 'findKey' function with a sample object and testing function
console.log(findKey(
  {
    barney: { age: 36, active: true },
    fred: { age: 40, active: false },
    pebbles: { age: 1, active: true }
  },
  o => o['active'] // Check if the 'active' property of the object is true
)); // Output: 'barney'

Output:

barney

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-236-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that returns the first key in an object that satisfies a given predicate function.
• Write a JavaScript function that iterates over an object's keys and returns the first key for which the callback is true.
• Write a JavaScript program that uses Object.keys() and Array.find() to retrieve the first matching key.
• Write a JavaScript function that searches through an object's properties and returns the key that first meets a condition.

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