d0norSexa

const arr1 = ['x','y'];
const  arr2 = ['y','z'];
const  arr3 = ['x', 'z'];
const arr4 =['x','y','z','c'];

const newarr = [].concat(arr1, arr2, arr3, arr4);
let result = {};

for (let elem of newarr) {
	if (result[elem] === undefined) {
		result[elem] = 1;
	} else {
		result[elem]++;
	}
}

console.log(result);

let allArr = [].concat(arr1, arr2, arr3, arr4)

let result = allArr.reduce((acc, cur) => {
    acc[cur] = acc[cur] ? acc[cur] + 1 : 1
    return acc
}, {})

console.log(result);