Having trouble retrieving properties from a JavaScript JSON object?

I am currently working with a JSON object that contains properties for MAKEs, MODELs, YEARs, STATEs, PLATEs, and COLORs. There are 4 instances of each property within the object:

Object {MAKE1="xxx ", MODEL1='xxx', YEAR1='xxx', STATE1='xxx', PLATE1='xxx', COLOR1='xxx', MAKE2='xxx', MODEL2='xxx' ,..., MAKE3='xx',..., MAKE4='xxx',...,COLOR4='xxx'}

In my JavaScript code:

 function displayPP() {
            $.getJSON('/ipad/api/formpp/' + personId + '/getmemberlatestpp', function(data) {

                for (var index=1; index<5; index++) {
                    $('#ppBody').append('<tr>');
                    var MAKE = 'MAKE' + index, MODEL = 'MODEL' + index, YEAR = 'YEAR' + index, STATE = 'STATE' + index, PLATE = 'PLATE' + index, COLOR= 'COLOR' + index;
                    var HTML = '<td>' + data.MAKE + '</td><td>' + data.MODEL + '</td><td>' + data.YEAR + '</td><td>' + data.STATE + '</td><td>' + data.PLATE + '</td><td>' + data.COLOR + '</td>';
                    $('#ppBody').append(HTML);
                    $('#ppBody').append('</tr>');      
                }                   
            });
    }

After running the code, I noticed that all the JSON properties returned as undefined. Can someone explain why this is happening? When accessing specific properties like data.MAKE1, data.MAKE2, etc., it works fine.

javascriptjson

Answer №1

When using <code>var foo = "X"; data.foo
, it will refer to the property named foo and not the property named X.

If you wish to use a variable to represent a property name, square bracket notation must be used (taking a string instead of an identifier).

data[foo]

It is advised to avoid having items with similar names except for a numerical counter at the end. It is recommended to use appropriate data structures:

[ 
    { 
        "make": "xxx", 
        "model": "xxx", 
        "year": "xxx", 
        "state": "xxx", 
        "plate": "xxx",
        "color": "xxx"
    },
    { 
        "make": "xxx", 
        "model": "xxx", 
        "year": "xxx", 
        "state": "xxx", 
        "plate": "xxx",
        "color": "xxx"
    }
]

Answer №2

To retrieve your property values, utilize bracket notation with a string input as demonstrated in the example below:

data['MAKE' + index]

Answer №3

When defining a variable, such as MAKE = 'MAKE1', make sure to use it correctly when accessing its value from an object like data.MAKE. Using dot notation in this case will look for a property named 'MAKE' within the data object. To access a variable using a string, you should utilize bracket notation instead, like data[MAKE].

Provided below is the updated version which rectifies all incorrect attempts at referencing properties with dots:

function displayPP() {
    $.getJSON('/ipad/api/formpp/' + personId + '/getmemberlatestpp', function(data) {
        for (var index=1; index<5; index++) {
            $('#ppBody').append('<tr>');
            var MAKE = 'MAKE' + index, MODEL = 'MODEL' + index, YEAR = 'YEAR' + index, STATE = 'STATE' + index, PLATE = 'PLATE' + index, COLOR= 'COLOR' + index;
            var HTML = '<td>' + data[MAKE] + '</td><td>' + data[MODEL] + '</td><td>' + data[YEAR] + '</td><td>' + data[STATE] + '</td><td>' + data[PLATE] + '</td><td>' + data[COLOR] + '</td>';
            $('#ppBody').append(HTML);
            $('#ppBody').append('</tr>');      
        }                   
    });
}

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