Javascript Try-Catch Performance Vs. Error Checking Code

Question

Would it be faster to just put code inside a try-catch block instead of performing various error checks?

For example..

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]; } 

VS

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;     } } 

I hope my question makes sense. I would be happy to clarify. Thank you!

Answer 1

"Programs must be written for people to read, and only incidentally for machines to execute."

Abelson & Sussman, SICP, preface to the first edition

Always aim for readable code. The key thing to remember is:

Avoid try-catch in performance-critical functions, and loops

Anywhere else they won't do much harm. Use them wisely, use them when they make sense.

But as I see you clearly misuse some functions for error checking. You can test for the desired objects and properties of objects right before you use them instead of complex checking. And:

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

can be written as

if (projectPhaseId != null) 

for example... So the example above can be fairly readable even without try catches. You seem to misuse YUI a bit.

I would bet this works as expected:

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  } 

How cool is that? :)