[ruslan_mart]

function filterByA(arr) {
   var res = [];

   for(var i = 0, item; i !== arr.length; i++) {
      item = arr[i];

      if(item != null && item.toString().charAt(0).toLowerCase() === 'a') {
           res.push(item);
      }
   }

   return res;
}


console.log( filterByA(['apple', 'banana', 'orange', 'avocado', 'cheese']) );

const filterByA = arr => {
    const res = [];

    for(let item of arr) {
        if(item != null && item.toString().startsWith('A')) {
              res.push(item);
        }
    }

    return res;
}

console.log( filterByA(['Apple', 'Banana', 'Orange', 'Avocado', 'Cheese']) );

const arrayStartsWith = by => arr => {
	const res = [];

	for(let item of arr) {
		if(item != null && item.toString().startsWith(by)) {
			res.push(item);
		}
	}

	return res;
};


const filterByA = arrayStartsWith('A');
const filterByB = arrayStartsWith('B');

let testArr = ['Apple', 'Banana', 'Orange', 'Avocado', 'Cheese', 'Black Chocolate'];


console.log( filterByA(testArr) );
console.log( filterByB(testArr) );