Question

192

How to add private variable to this Javascript object literal snippet?

rated 0 times [ 196] [ 4] / answers: 1 / hits: 15717 / 15 Years ago, tue, september 8, 2009, 12:00:00

Found this at MDC but how if I'd wanted to add a private variable to the

var dataset = {

    tables:{

        customers:{

            cols:[ /*here*/ ],

            rows:[ /*here*/ ]

        },

        orders:{

            cols:[ /*here*/ ],

            rows:[ /*here*/ ]

        }

    },

    relations:{

        0:{

            parent:'customers', 

            child:'orders', 

            keyparent:'custid', 

            keychild:'orderid',

            onetomany:true

        }

    }

}

The way I understand OOP in Javascript, I'd have access to dataset.tables.customers.cols[0] if such an item exists.

But if I wanted to place a private variable into customers, what would that look like?

Adding var index = 0; results in a runtime error.

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pariss

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2 Years ago

answered 15 Years ago mira · Accepted Answer

You can't have private variables without a function involved. Functions are the only way to introduce a new scope in javascript.

But never fear, you can add functions in the right place to gain this sort of functionality with your object

var dataset = {

  tables: {

    customers:(function(){

      var privateVar = 'foo';

      return { 

        cols:[ /*here*/ ],

        rows:[ /*here*/ ]

      }

    }()),

    orders:{

      cols:[ /*here*/ ],

      rows:[ /*here*/ ]

    }

  },

  relations: [{

    parent:'customers', 

    child:'orders', 

    keyparent:'custid', 

    keychild:'orderid',

    onetomany:true

  }]

};

But this doesn't gain us much. This is still mostly just a bunch of literal objects. These types of Private variables have zero meaning since there are no methods - nothing that would actually read or otherwise use the variables in the scope we created by adding a function (a closure).

But if we had a method, that might actually start to become useful.

var dataset = {

  tables: {

    customers:(function(){

      var privateVar = 'foo';

      return { 

        cols:[ /*here*/ ],

        rows:[ /*here*/ ],

        getPrivateVar: function()

        {

          return privateVar;

        }

      };

    }()),

    orders:{

      cols:[ /*here*/ ],

      rows:[ /*here*/ ]

    }

  },

  relations: [{

    parent:'customers', 

    child:'orders', 

    keyparent:'custid', 

    keychild:'orderid',

    onetomany:true

  }]

};



alert( dataset.tables.customers.getPrivateVar() );