CODEWITHSUNDEEP
javascriptnode.jscoffeescript
Eamorr
Eamorr

Reputation: 10012

Elegant Javascript code for checking undefined values

So I have a callback function which provides a json object:

function(object){
    var data=object.packet.link.ip.tcp.data;
    console.log(data.toString());
}

The problem I have is that any of packet/link/ip/tcp/data can be "undefined" - my node.js program falls over every time it hits an undefined variable.

I tried putting the declaration of "data" inside try/catch, however I keep getting "undefined" errors - my guess is that I'd need to put object/object.packet/object.packet.link/object.packet.link.ip/etc. in try/catch.

So, I found some elegant coffeescript:

if object?.packet?.link?.ip?.tcp?.data? then doStuff()

which compiles to:

var _ref, _ref1, _ref2, _ref3;

if ((typeof object !== "undefined" && object !== null ? (_ref = object.packet) != null ? (_ref1 = _ref.link) != null ? (_ref2 = _ref1.ip) != null ? (_ref3 = _ref2.tcp) != null ? _ref3.data : void 0 : void 0 : void 0 : void 0 : void 0) != null) {
       //doStuff:
       var data = object.packet.link.ip.tcp.data;
       console.log(data.toString());
}

Yuck!

Now it works perfectly, but I was just wondering if there's a more elegant (readable) way of doing this in pure Javascript?

Upvotes: 3

Views: 376

Answers (3)

jAndy
jAndy

Reputation: 235972

If it is just enough to check whether or not you're dealing with truthy values, you might go like

var data = object && object.packet && object.packet.link && object.packet.link.ip; // etc.

still no beauty, but most likely the best you can go for. Of course, you always have the option of introducing the good ol' try..catch clause.

try {
    var data = object.packet.link.ip.tcp.data;
} catch( ex ) { }

Anything "better" than that in terms of "elegance" (whoever that defines) would require a custom written function, which walks step by step through the object properties, checking for existence.

Upvotes: 3

Aravind
Aravind

Reputation: 3179

function A(object)
{
 var data = object?object.packet?object.packet.link?object.packet.link.ip?object.packet.link.ip.tcp?  object.packet.link.ip.tcp.data:null:null:null:null:null;
 console.log(data);
}

  • Note:

    If data has null, you can't call toString on null, as null(along with undefined) are the only two primitives which have no object wrappers and subsequently no toString() functions.

Upvotes: 1

Karolis Juodelė
Karolis Juodelė

Reputation: 3770

You can do

["packet", "link", "ip", "tcp", "data"]
  .reduce(function (m, i) { if (m) return m[i]; }, object);

You could move the reduce into a function and have get(object, "packet", "link", "ip", "tcp", "data"). It can be pretty, although a simple && solution might be more sensible.

Upvotes: 5

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