Default Values for JSON in javascript

Question

In the code:

slider.init({
 foo: "bar"
});

var slider={
 init:function(data){
 }
}

If I use data.foo, I will get "bar".

Supposing I have an optional variable called fish which can be included in the JSON variable. If I reference data.fish, I will be told that it is undefined or an error will be thrown or something. Is there a way that I can assign a default value to fish so that when I request data.fish, even though it is not set in the parameter, I will get a default value?

Solution

You can use the or operator to assign default values in case the aren't defined, for example:

var slider = {
 init:function(data){
   var fish = data.fish || "default value";
 }
}

Or you can make an "extend" function, to merge two objects, similar to the jQuery extend function:

function extend (obj1, obj2) { 
  var result = obj1, val;
  for (val in obj2) {
    if (obj2.hasOwnProperty(val)) {
      result[val] = obj2[val];
    }
  }
return result;
}

var defaults = {val1: 1, val3: 3, fish: 'fish'};
extend(defaults, {val2: 2}); // returns Object val1=1 val3=3 fish=fish val2=2

Comments

[Vnuk]

This is very good concept, I had no idea that you could do this, thanks.

[jcuenod]

lol, thanks - I was thinking about something like that but just couldn't put my finger on it - I also thought that it might throw errors because data.fish would be null and it wouldn't want to be compared