1. 格式转换：3,456,123转为3456123

function formatStr(str){
    return str.replace(/,/g,'');
}
//demo
var str = '3,456,123'
console.log(formatStr(str))

2.格式转换：如3456123转为3,456,123

function formatNum(num){
    var str_num = num + '';//转换成字符串
    var ret_num = '';
    var counter = 0;
    for(var i=str_num.length-1;i>=0;i--){
        ret_num = str_num.charAt(i) + ret_num;
        counter++;
        if(counter==3){
            counter = 0;
            if(i!=0){
                ret_num = ',' + ret_num;
            }
        }
    }
    return ret_num;
}
// demo:
var num = 3456123;
console.log(formatNum(num));

3. 随机数生成

        var rnd1 = Math.random();//返回0~1任意小数
        console.log(rnd1)
        var rnd2 = Math.floor(Math.random()*33);//返回0~33之间任意整数
        console.log(rnd2)

4. 格式化显示数字

        var pi = 3.14159;
        console.log(pi.toFixed(2));//保留2位小数
        console.log(pi.toPrecision(9));//从左到右保留9位数字，不够补0

5. 小数转整数

        var f = 1.5;
        console.log(Math.round(f));//四舍五入
        console.log(Math.ceil(f));//返回大于f的最小整数
        console.log(Math.floor(f));//返回小于f的最大整数

6.实现字符串长度截取并在字符串后添加...

        function cutstr(str, len) {
            var temp;
            var icount = 0;
            var patrn = /[^\x00-\xff]/;  //表示汉字或者全角，即ASCII 编码不在0-255的字符
            var strre = "";
            for (var i = 0; i < str.length; i++) {
                if (icount < len) {
                    // 每次截取一个字符
                    temp = str.substr(i, 1);
                    if (patrn.exec(temp) == null) {
                        // 如果是英文、半角
                        icount = icount + 1
                    } else {
                        // 如果是中文、全角
                        icount = icount + 2
                    }
                    // 字符串连接
                    strre += temp
                } else {
                    break
                }
            }
            return strre + "..."
        }
        // demo:
        console.log(cutstr("Tianzhihong", 4));
        console.log(cutstr("我是中国人", 5));

7. 获取主域名

        function getHost(url) {
            var host = "null";
            if(typeof url == "undefined"|| null == url) {
                url = window.location.href;
            }
            var regex = /^\w+\:\/\/([^\/]*).*/;
            var match = url.match(regex);
            if(typeof match != "undefined" && null != match) {
                host = match[1];
            }
            return host;
        }
        // demo:
        console.log(getHost("https://www.baidu.com/s?ie=utf-8&f=3&rsv_bp=0&rsv_idx=1&tn=baidu&wd=%E4%B8%B4%E6%97%B6%20%E8%8B%B1%E6%96%87&rsv_pq=fe2c6b690033543f&rsv_t=e826BZYU7Lfmea068KJo57JWFCFA91Cos63Q9PCwIFlVuebah2RSbB0O94E&rqlang=cn&rsv_enter=1&rsv_sug3=8&rsv_sug1=7&rsv_sug7=100&rsv_sug2=0&prefixsug=%25E4%25B8%25B4%25E6%2597%25B6%2520&rsp=0&inputT=9138&rsv_sug4=10044"))

8. 清除左右空格

        function trim(str){
            return str.replace(/(^\s*) | (\s*$)/g,"")
        }
        console.log(trim('tian   '));

9. 时间日期格式转换

        Date.prototype.Format = function(formatStr) {
            var str = formatStr;
            var Week = ['日', '一', '二', '三', '四', '五', '六'];
            str = str.replace(/yyyy|YYYY/, this.getFullYear());
            str = str.replace(/yy|YY/, (this.getYear() % 100) > 9 ? (this.getYear() % 100).toString() : '0' + (this.getYear() % 100));
            str = str.replace(/MM/, (this.getMonth() + 1) > 9 ? (this.getMonth() + 1).toString() : '0' + (this.getMonth() + 1));
            str = str.replace(/M/g, (this.getMonth() + 1));
            str = str.replace(/w|W/g, Week[this.getDay()]);
            str = str.replace(/dd|DD/, this.getDate() > 9 ? this.getDate().toString() : '0' + this.getDate());
            str = str.replace(/d|D/g, this.getDate());
            str = str.replace(/hh|HH/, this.getHours() > 9 ? this.getHours().toString() : '0' + this.getHours());
            str = str.replace(/h|H/g, this.getHours());
            str = str.replace(/mm/, this.getMinutes() > 9 ? this.getMinutes().toString() : '0' + this.getMinutes());
            str = str.replace(/m/g, this.getMinutes());
            str = str.replace(/ss|SS/, this.getSeconds() > 9 ? this.getSeconds().toString() : '0' + this.getSeconds());
            str = str.replace(/s|S/g, this.getSeconds());
            return str;
        }
        function convertDate(str){
            var date = new Date(str);
            return date.Format('yyyyMMdd'); //这里写需要的转换格式
        }
        console.log(convertDate('2017-03-12'));

10. 加载样式文件

        function loadStyle(url){
            try{
                document.creatStyleSheet(url);
            }catch(e){
                var linkcss = document.createElement('link');
                linkcss.type = 'text/css';
                linkcss.rel = 'stylesheet';
                linkcss.href = url;
                var head = document.getElementsByTagName('head')[0];
                head.appendChild(linkcss);
            }
        }
        loadStyle('css/style.css');

11. 十六进制颜色值的随机生成

//js
        function randomColor(){
            var arrHex=["0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f"],
                strHex="#",
                index;
                for(var i=0;i<6;i++){
                    index=Math.floor(Math.random()*16);
                    strHex+=arrHex[index];
                }
            return strHex;
        }
        document.getElementById('text').style.color = randomColor();
//html
<p id="text">我是中国人</p>