let btn = document.querySelector('.b-1');
let out = document.querySelector('.out-1');
let a6 = [
[1, 2],
[3, 4],
[5, 6]
];
btn.onclick = function f6() {
let arr = [];
for (let i = 0; i < a6.length; i++) {
for (let k = 0; k < a6[i].length; k++) {
arr.push(a6[i][k]);
console.log(arr[i][k]);
}
}
}