Fibonacci secuence as letters

fibletter

function* fibletter() {
    let a = 0;
    let b = 1;
    while(true) {
        yield String.fromCharCode(97 + ((b-1)%26));
        [a,b] = [b,b+a]
    }
}

gen = fibletter(); for(let a = 1; a < 10; a++) {console.log(Array(6).fill(1).map(v =>  gen.next().value).join``)}