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

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

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:

//#Source https://bit.ly/2neWfJ2 
const findKey = (obj, fn) => Object.keys(obj).find(key => fn(obj[key], key, obj));

console.log(findKey(
  {
    barney: { age: 36, active: true },
    fred: { age: 40, active: false },
    pebbles: { age: 1, active: true }
  },
  o => o['active']
));

Sample Output:

barney

Flowchart:

flowchart: Get the first key that satisfies the provided testing function.

Live Demo:

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


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JavaScript: Tips of the Day

Hide DOM Elements Dynamically

DOM elements can be done dynamically using JavaScript.
We can use the stykle.display property to do it.
For instance, we can write :

element.style.display = 'none';

It's the same as setting display: 'none'.
If we want to toggle them element back on, we can write:

element.style.display = 'block'

Ref: https://bit.ly/3mp5NgH