var a = [ "We're up all night 'til the sun", "We're up all night to get some", "We're up all night for good fun", "We're up all night to get lucky"];// These two assignments are equivalent:// Old-school:var a2 = a.map(function(s){ return s.length });// ECMAscript 6 using arrow functionsvar a3 = a.map( s => s.length );// both a2 and a3 will be equal to [31, 30, 31, 31]