JavaScript: Get the last key that satisfies the provided testing function, otherwise undefined is returned
JavaScript fundamental (ES6 Syntax): Exercise-235 with Solution
Write a JavaScript program to get the last key that satisfies the provided testing function, otherwise undefined is returned.
- Use Object.keys(obj) to get all the properties of the object.
- Use Array.prototype.reverse() to reverse the order and Array.prototype.find() to test the provided function for each key-value pair.
- The callback receives three arguments - the value, the key and the object.
Sample Solution:
JavaScript Code:
//#Source https://bit.ly/2neWfJ2
const findLastKey = (obj, fn) =>
Object.keys(obj)
.reverse()
.find(key => fn(obj[key], key, obj));
console.log(findLastKey(
{
barney: { age: 36, active: true },
fred: { age: 40, active: false },
pebbles: { age: 1, active: true }
},
o => o['active']
));
Sample Output:
pebbles
Flowchart:

Live Demo:
See the Pen javascript-basic-exercise-235-1 by w3resource (@w3resource) on CodePen.
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