Here you can find the source of underscore()
String.prototype.underscore = function() { return this.trim().toLowerCase().replace(/[\s]+/g, '_'); }
String.prototype.toUnderscore = function() { var str = this.replace(/[A-Z]/g, function(s) { return "_" + s.toLowerCase(); }); while (str.charAt(0) === '_') { str = str.slice(1); return str; }; ...
String.prototype.toUnderscore = function() { var str = this; var modified = ''; for (var i = 0; i < str.length; i++) { if (isLower(str[i])) { modified += str[i]; } else { if (str.length > i-1) { if (isLower(str[i-1])) { ...
String.prototype.underscore = function() { return this.replace(/([a-z\d])([A-Z]+)/g, '$1_$2').replace(/[-\s]+/g, '_').toLowerCase(); };
String.prototype.underscore = function() { return this.gsub(/::/, '/').gsub(/([A-Z]+)([A-Z][a-z])/,'#{1}_#{2}').gsub(/([a-z\d])([A-Z])/,'#{1}_#{2}').gsub(/-/,'_').toLowerCase(); };
String.prototype.underscore = function() { return this .replace(/::/g, '/') .replace(/([A-Z]+)([A-Z][a-z])/g, '$1_$2') .replace(/([a-z\d])([A-Z])/g, '$1_$2') .replace(/-/g, '_') .toLowerCase(); };
String.prototype.underscore = function () { var str = this; str = str.replace(/([A-Z]+)([A-Z][a-z])/g, '$1_$2'); str = str.replace(/([a-z\d])([A-Z])/g, '$1_$2'); str = str.replace(/\-/g, '_'); return str.toLowerCase(); };
String.prototype.underscorize = function() { return this.replace(/([A-Z])/g, function($1) { return "_" + $1.toLowerCase(); }).replace(/^_/g, ""); };