var s = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890';
function f(s, width){
return s.replace(
new RegExp('[\\s\\S]{1,'+(width || 4)+'}', 'g'),
function(m){
return '^' + new Array(m.length).join(' ');
});
}
console.log(s);
console.log(f(s, 4));
console.log(f(s, 8));