Javascript Try-Catch 性能对比。错误校验码

Question

将代码放在 try-catch block 中而不是执行各种错误检查会更快吗？

例如..

function getProjectTask(projectTaskId) {
    if (YAHOO.lang.isUndefined(projectTaskId) || YAHOO.lang.isNull(projectTaskId) && !YAHOO.lang.isNumber(projectTaskId)) {
        return null;
    }

    var projectPhaseId, projectPhaseIndex, projectTaskIndex, projectPhases, projectPhase, projectTask;

    if (!YAHOO.lang.hasOwnProperty(projectTaskPhaseMap, projectTaskId)) {
        return null;
    }

    projectPhaseId = projectTaskPhaseMap[projectTaskId];

    if (YAHOO.lang.isUndefined(projectPhaseId) || YAHOO.lang.isNull(projectPhaseId) || !YAHOO.lang.hasOwnProperty(scheduleData.ProjectPhasesMap, projectPhaseId)) {
        return null;
    }

    projectPhaseIndex = scheduleData.ProjectPhasesMap[projectPhaseId];
    if (YAHOO.lang.isUndefined(projectPhaseIndex) || YAHOO.lang.isNull(projectPhaseIndex) || !YAHOO.lang.hasOwnProperty(scheduleData.ProjectPhases[projectPhaseIndex])) {
        return null;
    }
    projectPhase = scheduleData.ProjectPhases[projectPhaseIndex];

    if (!YAHOO.lang.hasOwnProperty(projectPhase.ProjectTasksMap, projectTaskId)) {
        return null;
    }

    projectTaskIndex = projectPhase.ProjectTasksMap[projectTaskId];

    if (YAHOO.lang.isUndefined(projectTaskIndex) || YAHOO.lang.isNull(projectTaskIndex)) {
        return null;
    }

    projectTask = scheduleData.ProjectTasks[projectTaskIndex];
}

对比

function getProjectTask(projectTaskId) {
    try {
        projectPhaseId = projectTaskPhaseMap[projectTaskId];
        projectPhaseIndex = scheduleData.ProjectPhasesMap[projectPhaseId];
        projectPhase = scheduleData.ProjectPhases[projectPhaseIndex];
        projectTaskIndex = projectPhase.ProjectTasksMap[projectTaskId];
        projectTask = scheduleData.ProjectTasks[projectTaskIndex];

    }
    catch (e) {
        return null;
    }
}

我希望我的问题是有道理的。我很乐意澄清。谢谢!

Answer 1

"Programs must be written for peopleto read, and only incidentally formachines to execute."

Abelson & Sussman, SICP, preface to the first edition

始终以可读代码为目标。要记住的关键是:

避免在性能关键函数和循环中使用 try-catch

它们不会对其他任何地方造成太大伤害。明智地使用它们，在它们有意义时使用它们。

但正如我所见，您显然滥用了一些函数来进行错误检查。您可以在使用它们之前测试所需的对象和对象的属性，而不是进行复杂的检查。并且:

if (YAHOO.lang.isUndefined(projectPhaseId) || YAHOO.lang.isNull(projectPhaseId))

可以写成

if (projectPhaseId != null)

例如...所以即使没有 try catches，上面的示例也可以相当可读。您似乎有点滥用 YUI。

我敢打赌这会像预期的那样工作:

function getProjectTask(projectTaskId) {

   var projectPhaseId    = projectTaskPhaseMap[projectTaskId],
       projectPhaseIndex = scheduleData.ProjectPhasesMap[projectPhaseId],
       projectPhase      = scheduleData.ProjectPhases[projectPhaseIndex];

  if (projectPhase == null) return null; // projectPhase would break the chain

  var projectTaskIndex  = projectPhase.ProjectTasksMap[projectTaskId],
      projectTask       = scheduleData.ProjectTasks[projectTaskIndex];

   return projectTask || null; // end of the dependency chain

}

这有多酷？ :)