_.map = _.collect = function(obj, iteratee, context) {iteratee = cb(iteratee, context);// 這里的keys是希望得到一個數組吧，而實際源碼中會得到一個Boolean值// 是否應該換成這種寫法？keys = !isArray(obj) ? _.keys(obj) : void 0var keys = !isArrayLike(obj) && _.keys(obj),      length = (keys || obj).length,    results = Array(length);for (var index = 0; index < length; index++) {  var currentKey = keys ? keys[index] : index;  results[index] = iteratee(obj[currentKey], currentKey, obj);}return results;};