Javascript Object: Map of Functions. How to return default value

Question

Sorry for the title of this question, but I don't found a better one.

INTRODUCTION

My goal is to create an object, and associate to every params a function. Very simple!

var canIDoThis = {
    one: function(a, b, c){},
    two: function(a){},
    three: function(){}
}

I want call canIDoThis in this way

if(canIDoThis['one'](x, y, z)) {
    // do somthing
}

if(canIDoThis['two'](w)) {
    // do somthing
}

if(canIDoThis['three']()) {
    // do somthing
}

If I have a var that can be "one", "two" or "three" I can use this canIDoThis in this way

// myVariable can be equalso to "one" or "two" or "three"
var myVarable;

if(canIDoThis[myVarable]()) {
    // do somthing
}

MY PROBLEM

I'd like to manage all myVarable value. Now if I call canIDoThis['four']() I get obviously Uncaught TypeError: undefined is not a function

MY QUESTION

Is there a way to prevent the default behaviour of Uncaught TypeError and return a default value? It would be cute if canIDoThis['four']() be interpretated as false or undefined

PS: I would like do this in pure JavaScript ;)

Why not to use object-oriented way with creating a class-function with getters and stuff? — VisioN
– VisioN, Commented May 29, 2014 at 15:49
Object Oriented Way is the most correct way, in my opinion... ;) I war searching a different way. Link add some custom exception handler or something like this. But maybe it's not as simple... Anyway I done it with OO way :) — RikyTres
– RikyTres, Commented May 30, 2014 at 9:44
You'd probably post your solution as an answer here, so others may see the way you found useful and problem solving. — VisioN
– VisioN, Commented May 30, 2014 at 9:48

Pudge601 · Accepted Answer · 2014-05-29 15:49:38Z

1

Try checking if the property is a function before calling it using typeof.

if (typeof(canIDoThis[myVarable]) === 'function') {
    canIDoThis[myVarable]();
}

answered May 29, 2014 at 15:49

Pudge601

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Comments

RikyTres · Accepted Answer · 2014-05-30 10:02:31Z

1

All solutions posted was good turnaround for the problem, but I was searching for something like "Cath the exception and handle it" or "set a default behaviour"...

But this way seem to be not possible.

I prefered to use an Object-Oriented style solution.

This is the solution...

function Context(type) {
    var _type = type,
        // all the functions in config returs true or false, depens on the value of p
        _config = {
            one: function(p){},
            two: function(p){},
            three: function(p){}
        },
        _defaultBehaviour = function() {return false;}
    this.canIDoThis = function(param){
        var fn = this._config[_type] || _defaultBehaviour;
        return fn(param);
    }
}

and then use it in this way

// type can be absolutly anything
var type,
    param = {/*some dynamic params in an Object*/},
    context = new Context(type)

if (context.canIDoThis(params)) {
    // good! Let's go!
} else {
    // stop, access not allowed!
}

This solution work really good for my use case, but It could be improved.

answered May 30, 2014 at 10:02

RikyTres

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1 Comment

VisioN Over a year ago

Yes, this is the way to do the things.

Trevor Dixon · Accepted Answer · 2014-05-29 15:49:16Z

0

Check that it's not undefined before trying to call it.

// myVariable can be equalso to "one" or "two" or "three"
var myVarable;
var fn = canIDoThis[myVarable];

if(fn && fn()) { // Only invokes fn if it's not falsey; if it's undefined, it won't try to call it
    // do somthing
}

Check to see if canIDoThis[myVarable] has a value before trying to call it.

answered May 29, 2014 at 15:49

Trevor Dixon

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Comments

gen_Eric · Accepted Answer · 2014-05-29 15:51:36Z

0

Instead of an object, use a "getter" function. That way you can check if the method exists before you try and call it.

function getValue(name){
    var canIDoThis = {
        one: function(a, b, c){},
        two: function(a){},
        three: function(){}
    }

    if(typeof canIDoThis[name] === 'function'){
        return canIDoThis[name].apply(canIDoThis, [].slice.call(arguments, 1));
    }
    else{
        return false;  // Default return value
    }
}

Then you can do getValue('one', x, y, z); or getValue('four');.

answered May 29, 2014 at 15:51

gen_Eric

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