在JS文件中使用Ajax获取JSON数据

Question

我对javascript不太满意，下面是我想从JSON获取变量并将日期放在图表上作为标签的代码。下面是代码

function getdate(num){
$.ajax({                              
		  url: 'http://81.12.18.111/fibarobiz/showjson.php',
		  data: "device=41", 
		  dataType: 'json', 
		  	
          success: function(data)         
          {
         var aMon= data.date[num]; 
		 // var aMon = '2/18';
			return aMon;    <--no value to return
           //    var pmvalue =data.properties.value;
			//			$('#pm25v').append( pmvalue );
   
				   } 
					
        });
}
$(function() {
    "use strict";
	var Mon=getdate(0); <-- outcome always undefined
    // ============================================================== 
    // Revenue
    // ============================================================== 
 var ctx = document.getElementById('revenue').getContext('2d');
            var myChart = new Chart(ctx, {
                type: 'line',

                data: {
                    //labels: ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'],
					labels: [Mon, 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'],
                    datasets: [{
                        label: 'Current Week',
                        data: [12, 19, 3, 17, 6, 3, 7],
                      backgroundColor: "rgba(89, 105, 255,0.5)",
                                    borderColor: "rgba(89, 105, 255,0.7)",
                                    borderWidth: 2
                        
                    }
                    ......

无论我为变量“ aMon”使用静态值，都不能返回任何值。我认为它不能在JS文件中运行Ajax吗？请帮忙！！非常感谢！

威尔逊