Using a try catch around an object literal

Question

Inside a callback I build an object I build to send out in my Express app:

this.response = {
      owner: data.actions[1].causes[0].shortDescription,
      build_version: data.actions[0].parameters[0].value,
      branch_to_merge: data.actions[0].parameters[1].value,
      jira_tickets: data.actions[0].parameters[2].value,
      build_description: data.actions[0].parameters[3].value,
      outcome: data.result
    };

If I get a different response than what I'm used to I get a fatal cannot find 'property' of undefined error that crashes my server caused by these: data.actions[1].causes[0].shortDescription.

I was wondering what to do about it and I thought I could just put it in a try catch but that seems wrong.

What's considered a good way of dealing with this?

Answer 1

1. use try/catch

In your statement you have:

• 26 potential sources for Reference errors (16 missing objects, 10 array out of bounds).

That's what try/catch handles best. Dealing with the same type of error from a block of code and handling in one place. So unless you want to deal with each potential error individually, try/catch is the simplest and best tool you at your disposal. It works and you can pinpoint the problem:

var w = {}
try {w.x.y.z} catch(e) {e}

TypeError: Cannot read property 'y' of undefined(…)

Alternatively, if you need more control, you could

2. test all references up-front

If it must succeed even if some properties fail, you can check each reference. e.g.:

var sdValid = data && 
            data.actions && 
            data.actions.length>1 && 
            data.actions[0].causes && 
            data.actions[0].causes.length && 
            data.actions[1].causes[0].shortDescription;
var owner = sdValid
            ?  data.actions[1].causes[0].shortDescription 
            : 'default value';
this.response = {
    owner : owner,
    // etc... 
}

You can easily make it more readable if you

3. roll out your own reference checker

this.response = {
    owner : nestget(data, 'nobody')
               .prop('actions', 1)
               .prop('causes', 0)
               .prop('shortDescription')
               .value(), 
               // return shortDescription if you got this far or 'nobody'

    build_version : nestget(data, '0.0.0')
               .prop('actions', 0)
               .prop('parameters', 0)
               .prop('value')
               .value(),
               // return value if you got this far or '0.0.0'
    // ... etc
};

// Custom - easy to use reference checker
function nestget (obj, default) {
   var valid = false;
   this.default = default;
   this.obj = obj;
   var that = this;

   return { 
       prop : propChecker,
       value : getValue
   }

   function propChecker (prop, i) {
      // implementation omitted for brevity
   }
   function getValue () {
      return value;
   }
}

4. use a library

Last but not least, you can always use a library. Personally I like how XPath searches XML trees so I would suggest using something like JSONPath to search for nested objects in a data structure. e.g.

this.response = {
    owner : jsonpath(data, '$..shortDescription[0]'),
    build_version jsonpath(data, '$.actions[0].parameters[0].value'), // no error
    // ... etc
}

However, there are lots of options out there (e.g. lodash/underscore as mentioned in a comment).