optify.js - refactor long function parameters into "pass an opts object" style

optify.js

/*
 * optify.js - refactor long function parameters into "pass an opts object" style
 *
 * vim instructions:
 * 1) Using shift-v, select `function (a,b,c,d,e,cb) {`
 * 2) Type ":!node ~/optify"
 * 3) Selection is replaced with:
 *   function (opts,cb) {
 *     var a = opts.a;
 *     var b = opts.b;
 *     ...
 */
var code = '';
stdin.on('data', function(chunk) { code += chunk.toString('utf8'); });                         
stdin.on('end', optify);                                                                       
stdin.resume();                                                                                
  
var FUNC = /^(\s*)(.*?function[^\)]+\()([^\)]*)(\)\s*\{)/;                                     
var CB = /(?:^cb|^next|^callback|^continuation|(?:cb))$/i                                      
function optify() {
  var match = code.match(FUNC);                                                                
  if (!match) {
    stdout.write(code);
    return;
  }

  var indent = match[1];
  var declIndent = (indent !== undefined && indent.length) ? indent : '  ';
  var funcDecl = match[2];
  var rawParams = match[3];
  var blockStart = match[4];

  var leadIn = match.index > 0 ? code.substr(0, match.index) : '';
  var leadOut = code.substr(match.index + match[0].length, code.length);

  var params = rawParams.split(/\s*,\s*/);
  var isCPS = CB.test(params[params.length-1]); // Continuation Passing Style

  var newParams = 'opts';
  if (isCPS) newParams += ', '+params.pop();

  if (params.length === 1 && params[0] === '') params = [];

  var newDecls = params.map(function(param) {
    return "\n"+indent+declIndent+"var "+param+" = opts."+param+";"
  }).join('');

  stdout.write(leadIn + indent + funcDecl + newParams + blockStart + newDecls + leadOut);
}