This is the solution to the first task of JavaScript Minna Internship

task1.js

/**
STEP 1
- Check each letter in the sentence
- Check if it's uppercase
- If it's upper case, convert it to lower case and vice versa  
*/

const isLowerCase = ( letter ) => {
	const regex = /[a-z]/g;
	const reg = new RegExp(regex);
	return reg.test(letter);
}

const transposeCase = ( sentence ) => {
	let sentenceArray = sentence.split('');
	sentenceArray = sentenceArray.map(item => {
		if(isLowerCase(item)){
			return item.toUpperCase();
		} else {
			return item.toLowerCase();
		}
	})

	return sentenceArray.join('');
}

const filterUpperCasedWords = ( sentence ) => {
	let sentenceArray = sentence.split(' ');
	const filteredWords = sentenceArray.filter(item => {
		return !isLowerCase(item[0]);
	})
	return filteredWords;
}

const ingWords = (sentence) => {
	let sentenceArray = sentence.split(' ');
	const filteredWords = sentenceArray.filter(item => {
		item = item.toLowerCase();
		return item.endsWith('ing');
	})
	return filteredWords;
}

const isPalindrome = ( words ) => {
	words = words.map(word => word.toLowerCase());
	const palidromes = words.filter(word => {
		return word == word.split('').reverse().join('');
	})

	return palidromes;
}

function task( sentence ){
	const transposedCase = transposeCase(sentence);
	const uppercased = filterUpperCasedWords(transposedCase);
	const ing = ingWords(sentence);
	const palindrome = isPalindrome(uppercased);


	const result = {
		uppercased,
		ing,
		palindrome,
	}
	return result;
}

const sentence = 'maDam aYOing Who Stays IniNg oYo Was in aING Bus to Lagos whEn Her Son Sold the rAceCar'
console.log(task(sentence));