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));