将数字金额格式化为每三个数加一个逗号的格式

function changeNum(num){
                var numArr=num.toString().split('.');
                var temArr=[];
                var lastArr=[];
                for (var i=numArr[0].length;i>0;i-=3) {
                    
                    temArr.unshift(numArr[0].substring(i-3,i));
                    
                }
                
                lastArr.push(temArr.join(','));
                lastArr.push(numArr[1]);
                
                return lastArr.join('.');
            }