Unfamiliar syntax in javascript object

Question

My question:


    var nsPreferences = {

    property1:"",

    get mPrefService()
        {
          return Components.classes["@mozilla.org/preferences-service;1"]
                           .getService(Components.interfaces.nsIPrefBranch);
        },

    setBoolPref: function (aPrefName, aPrefValue)
        {
          try 
            {
              this.mPrefService.setBoolPref(aPrefName, aPrefValue);
            }
          catch(e)
            {
            }
        },

    getBoolPref: function (aPrefName, aDefVal)// Prefs.jsで使用
        {
          try
            {
              return this.mPrefService.getBoolPref(aPrefName);
            }
          catch(e)
            {
              return aDefVal != undefined ? aDefVal : null;
            }
          return null;        // quiet warnings
        },


    };

In this object nsPreferences, what is this "get mPrefService(){}"? This is the first time I've seen this kind of syntax in javascript object. Would anyone tell me about this syntax?

They're getters and setters: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Working_with_Objects#Defining_getters_and_setters — Blender, Aug 02 '13 at 03:07
Have a look at http://stackoverflow.com/questions/5409372/does-javascript-have-get-set-keywords-like-c — Ranjith Ramachandra, Aug 02 '13 at 03:13
@Blender,@Ranjith R :Is it equivalent to "*** : function(){***;return ***;},"? Is there any merit in using get syntax, other than making code smaller? — user2640929, Aug 02 '13 at 04:35
@user2640929: Sure. They let you modify properties nicely. You could do `foo.bar = -12` and `bar`'s setter would throw an error saying that `-12` is an invalid value. — Blender, Aug 02 '13 at 04:55

bfavaretto · Answer 1 · 2013-08-02T03:14:56.993

2

It's a getter function. It will look like a variable when you read it:

var someService = nsPreferences.mPrefService;

It calls that function without using the regular invocation parens. You can also use the set operator to create a "setter" function for the same property:

set mPrefService(val){
    this.actualVal = val;
},

nsPreferences.mPrefService = "service";

edited Aug 02 '13 at 03:14

answered Aug 02 '13 at 03:09

bfavaretto

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i.e.you can write like this alternatively,can't you?: getmPrefService: function(){ return Components.classes["@mozilla.org/preferences-service;1"] .getService(Components.interfaces.nsIPrefBranch); } – user2640929 Aug 02 '13 at 04:14
If you use that, you'll need `var someService = nsPreferences.getmPrefService();` to retrieve the value. Note `()` at the end, getters don't use that, but regular functions require it. – bfavaretto Aug 02 '13 at 13:18

Unfamiliar syntax in javascript object

1 Answers1