adding to json property that may or may not exist

问题:

let say I want to do this:

  var dashboard = {};
  var page = "index";

  $('.check').click(function(){ 
    $(this).toggleClass("active").siblings().slideToggle('slow', function() {
        dashboard['pages'][page][$(this).closest('li').attr("id")]['show'] = $(this).is(":hidden") ? 'collapsed' : 'expanded';
    });
  }

I get an error saying:

Dashboard.pages is undefined

Is there away to dynamically add pages and the children that follow without having to do the work of checking to see if it is defined first then if it's not doing:

   dashboard['pages'] = {};

because sometimes they may already exist and I don't want to have to inspect the tree first I just want to build the branches as needed

EDIT I changed pagename to page to show that page names will change and also I want to point out that the pages could really be anything too. The idea is that you have any object that can contain objects with parameters without checking to see if the branches exist

It looks like $extend as stated will be the way to go just not sure how that works. Got to get my head around that.

回答1:

Define get and set methods on an Object. Actually it could be defined just on the dashboard object and only its descendants, but that's easy to do.

Object.prototype.get = function(prop) {
    this[prop] = this[prop] || {};
    return this[prop];
};

Object.prototype.set = function(prop, value) {
    this[prop] = value;
}

Iterate through nested properties using this get() method and call set() whenever a value has to be set.

var dashboard = {};

dashboard.get('pages').get('user').set('settings', 'oh crap');
// could also set settings directly without using set()
dashboard.get('pages').get('user').settings = 'oh crap';

console.log(dashboard); //​​​​​​​​​​​​​​​ {pages: {user: {settings: "oh crap"}}};

You could also extend/modify the get method to accept the nested properties as individual arguments or an array or a string. Using that, you'd only have to call get once:

// get accepts multiple arguments here
dashboard.get('pages', 'user').set('settings', 'something');

// get accepts an array here
dashboard.get(['pages', 'user']).set('settings', 'something');

// no reason why get can't also accept dotted parameters
// note: you don't have to call set(), could directly add the property
dashboard.get('pages.user').settings = 'something';

Update:

Since the get method generically returns an object and does not know whether you need an array or some other type of object, so you would have to specify that yourselves:

dashboard.get('pages.user').settings = [];

Then you could push items to the settings array as

dashboard.get('pages.user').settings.push('something');
dashboard.get('pages.user').settings.push('something else');

To actually have the get function construct the object hierarchy from a given string such as pages.user, you would have to split the string into parts and check if each nested object exists. Here is a modified version of get that does just that:

Object.prototype.get = function(prop) {
    var parts = prop.split('.');
    var obj = this;
    for(var i = 0; i < parts.length; i++) {
        var p = parts[i];
        if(obj[p] === undefined) {
            obj[p] = {};
        }
        obj = obj[p];
    }
    return obj;
}

// example use
var user = dashboard.get('pages.user');
user.settings = [];
user.settings.push('something');
user.settings.push('else');

console.log(dashboard); // {pages: {user: {settings: ["something", "else"] }}}

// can also add to settings directly
dashboard.get('pages.user.settings').push('etc');

回答2:

I would do it with the ternary operator:

dashboard['pages'][page] = dashboard['pages'][page] ? dashboard['pages'][page] : {};

That will do the trick no matter if it's set/null or whatever.

回答3:

I don't think there's a good builtin way to do this, but you could always abstract it with a function.

function getProperty(obj,prop){
    if( typeof( obj[prop] ) == 'undefined' ){
        obj[prop] = {};
    }
    return obj[prop];
}

Then you use

getProperty(dashboard,'pages')['pagename']

or

getProperty(getProperty(dashboard,'pages'),'pagename');

As mentioned, $.extend will make this less burdensome.

回答4:

The best solution for my case was to do a Object prototype

 /**
 * OBJECT GET
 * Used to get an object property securely
 * @param object
 * @param property
 * @returns {*}
 */
Object.get = function(object, property) {
    var properties = property.split('.');
    for (var i = 0; i < properties.length; i++) {
        if (object && object[properties[i]]) {
            object = object[properties[i]];
        }
        else {
            return null;
        }
    }
    return object;
};

And then you can get your property like this

var object = { step1: { step2: { step3: ['value1', 'value2'] }}}
Object.get(object, 'step1.step2.step3'); // ['value1', 'value2']
Object.get(object, 'step1.step2.step3.0'); // 'value1'
Object.get(object, 'step1.step2.step3.step4'); // null

Hope it helps :)

回答5:

var foo = dashboard['pages'] || {};
foo['pagename'] = 'your thing here';
dashboard['pages'] = foo;

Explaining: the first line will check if the first value is null, undefined or... false (don't think this is a problem here): if it is, create a new object, if it is not, will use it.

回答6:

$.extend is the way to go

function elem(a,b){
var r={'pages':{'pagename':{}}};
r.pages.pagename[a]={'show':b};
return r;
}
data={};
//inside the event handler or something:
data = $.extend(true,data,elem($(this).closest('li').attr("id"),$(this).is(":hidden") ? 'collapsed' : 'expanded'));

But honestly - this is a rather messy idea to store this information anyway. I bet that if You need that information later it could be done with a good selector or with jQuery.data()

回答7:

Well I guess you need this:

var dashBoard = new Array();
if(!dashboard['page123']) {
    dashBoard.push('page123');
} else {
...do what you want
}

Seems you are dealing with XML.

回答8:

If you use underscore >= 1.9.0, you can use property and propertyOf:

d={a: {b: "c"}}
_.property(["a", "b", "c", "e"])(d)   // undefined
_.property(["a", "b"])(d)             // "c"
_.propertyOf(d)(["a", "b", "c", "e"]) // undefined
_.propertyOf(d)(["a", "b"])           // "c"