如何在javascript中访问对象属性

Question

function test(results) {
        //Populate the ComboBox with unique values

        var Gov;
        var values = [];
        var features = results.features;
        var og;
        for (i = 0; i < features.length; i++) {

            var aGOV = {
                "GovName": features[i].attributes.ENG_NAME,
                "GovNO": features[i].attributes.GOV_NO,
                "Shape": features[i].geometry
            }
           og = new Option(features[i].attributes.ENG_NAME, aGOV);
            var cbx = document.getElementById("cbxGov");
            cbx.options.add(og);
        }

    }

    function gov_selection_change() 
    {
        var cbx = document.getElementById("cbxGov");

        var itm = cbx.options[cbx.selectedIndex].value.hasOwnProperty("Shape");
    }

html code

<select id="cbxGov" onchange="gov_selection_change()">

My problem is im not able to access property of aGOV in my gov_selection_change( ) function, it shows it has no such property, itm is false.

Answer 1

The variable aGOV is only available in the context of your result() function. If you want to use it from a different function declare it as a global variable.

Example:

var aGOV;

function result()
{
    // initialize aGOV
}

function gov_selection_change()
{
    // now you can access the aGOV variable
}

Answer 2

The value property of an HTMLOptionElement always returns a DOMString (aka text), not an object.

So you have to save what you want to access in a lookup dictionary and then use the returned value as a lookup key.

var lookupDictionary = {};

function test(results) {
    var lookupKey,
        og;
    //...

    // don´t get the element in the loop
    var cbx = document.getElementById("cbxGov");

    //...

    for (i = 0; i < features.length; i++) {
        lookupKey = features[i].attributes.GOV_NO;

        lookupDictionary[lookupKey] = {
            "GovName": features[i].attributes.ENG_NAME,
            "GovNO": features[i].attributes.GOV_NO,
            "Shape": features[i].geometry
        }

        og = new Option(features[i].attributes.ENG_NAME, lookupKey );
        cbx.options.add( og );
    }
}

function gov_selection_change() {
    var cbx = document.getElementById("cbxGov");
    var key = cbx.options[cbx.selectedIndex].value;
    var itm = lookupDictionary[key].hasOwnProperty("Shape");
}