function commafy() { var num = document.getElementById("NumA").value; //1.先去除空格,判断是否空值和非数 num = num + ""; num = num.replace(/[ ]/g, ""); if (num == "") { alert("空值，结束"); return; } if (isNaN(num)) { alert("非数，结束"); return; } //2.针对是否有小数点，分情况处理 var index = num.indexOf("."); if (index==-1) {//无小数点 var reg = /(-?\d+)(\d{3})/; while (reg.test(num)) { num = num.replace(reg, "$1,$2"); } } else { var intPart = num.substring(0, index); var pointPart = num.substring(index + 1, num.length); var reg = /(-?\d+)(\d{3})/; while (reg.test(intPart)) { intPart = intPart.replace(reg, "$1,$2"); } num = intPart +"."+ pointPart; } return alert(num); }