Exercício ES6

const classe1 = [{name: 'aluno1', sala: 'a'},{name: 'aluno2', sala: 'a'}];
const classe2 = [{name: 'aluno3', sala: 'b'},{name: 'aluno4', sala: 'b'}];
const classe3 = [{name: 'aluno5', sala: 'c'},{name: 'aluno6', sala: 'c'}];
const classe4 = [{name: 'aluno7', sala: 'd'},{name: 'aluno8', sala: 'd'}];
const classe5 = [{name: 'aluno9', sala: 'e'},{name: 'aluno10', sala: 'e'}];

const alunos = [...classe1, ...classe2, ...classe3, ...classe4, ...classe5];

const filter = alunos => sala => {
    return alunos.filter(aluno => aluno.sala === sala);
}

const filterBySala = filter(alunos);

console.log(filterBySala('d'));