CanvasJs not formatting date properly

Question

I want to display the number of patient diagnosed by cancer and from that I get my JSON data right. The problem is no matter what I do, it plots as date 1970 when the actual date is differen.
further more having checked that; when I include "JSON_NUMERIC_CHECK" on the PHP returned JSON, then will display the the Y-axis correctly and if I remove it will display the date correctly.

here is my JSON data

[
    {
        "y": 2,
        "x": 2004
    }
]

and here is my code

if(json.length !=0){
                //alert(json);
                    alert(json[0].x);


                    var dp1 = [];   
                    for(var i=0; i<json.length; i++){

                        dp1.push({x:new Date(json[i].x), y:json[i].y})
                    }

                            $("#dchart").CanvasJSChart({ //Pass chart options
                                title:{text:"Cancer Diagnosis Number "},
                                 zoomEnabled: true,
                                  panEnabled: true, 
                                    axisX:{valueFormatString:"YYYY",labelAngle:-45},

                                    data: [{
                                        color:"red",
                                        type: "column",
                                        legendText:"Thyroid Cancer",    
                                        showInLegend:true,
                                        dataPoints:dp1

                                        }]}); 

Answer 1

because of the "JSON_NUMERIC_CHECK" it converted both x and y to numbers, so I had to change the date number into string and than use the new Date() function on it.

as below

for(var i=0; i<json.length; i++){
                        var data = json[i].x;
                        var xd = String(data);
                        dp1.push({x:new Date(xd), y:json[i].y})