1.正则

// 匹配邮箱
let reg = /^([a-zA-Z]|[0-9])(\w|\-)+@[a-zA-Z0-9]+\.([a-zA-Z]{2,4})$

// (新)匹配手机号
let reg = /^1[0-9]{10}$/;

// (旧)匹配手机号
let reg = /^1(3|4|5|7|8)[0-9]{9}$/;

// 匹配8-16位数字和字母密码的正则表达式
let reg = /^(?![0-9]+$)(?![a-zA-Z]+$)[0-9A-Za-z]{8,16}$/;

// 匹配国内电话号码 0510-4305211
let reg = /\d{3}-\d{8}|\d{4}-\d{7}/;

// 匹配身份证号码
let reg=/(^\d{15}$)|(^\d{18}$)|(^\d{17}(\d|X|x)$)/;

// 匹配腾讯QQ号
let reg = /[1-9][0-9]{4,}/;

// 匹配ip地址
let reg = /\d+\.\d+\.\d+\.\d+/;

// 匹配中文
let reg = /^[\u4e00-\u9fa5]*$/;

2.检测平台（设备）类型

let isWechat = /micromessenger/i.test(navigator.userAgent),
    isWeibo = /weibo/i.test(navigator.userAgent),
    isQQ = /qq\//i.test(navigator.userAgent),
    isIOS = /(iphone|ipod|ipad|ios)/i.test(navigator.userAgent),
    isAndroid = /android/i.test(navigator.userAgent);

3.日期时间函数

// 时间格式化
function format_date(timeStamp) {
    let date = new Date(timeStamp);
    return date.getFullYear() + "年"
        + prefix_zero(date.getMonth() + 1) + "月"
        + prefix_zero(date.getDate()) + "日 "
        + prefix_zero(date.getHours()) + ":"
        + prefix_zero(date.getMinutes());
}

// 数字格式化
function prefix_zero(num) {
    return num >= 10 ? num : "0" + num;
}

// 倒计时时间格式化
function format_time(timeStamp) {
    let day = Math.floor(timeStamp / (24 * 3600 * 1000));
    let leave1 = timeStamp % (24 * 3600 * 1000);
    let hours = Math.floor(leave1 / (3600 * 1000));
    let leave2 = leave1 % (3600 * 1000);
    let minutes = Math.floor(leave2 / (60 * 1000));
    let leave3 = leave2 % (60 * 1000);
    let seconds = Math.floor(leave3 / 1000);
    if (day) return day + "天" + hours + "小时" + minutes + "分";
    if (hours) return hours + "小时" + minutes + "分" + seconds + "秒";
    if (minutes) return minutes + "分" + seconds + "秒";
    if (seconds) return seconds + "秒";
    return "时间到！";
}

4.跨端事件处理

// 是否支持触摸事件
let isSupportTouch = ("ontouchstart" in document.documentElement) ? true : false;

//禁用Enter键表单自动提交
document.onkeydown = function(event) {
    let target, code, tag;
    if (!event) {
        event = window.event; //针对ie浏览器
        target = event.srcElement;
        code = event.keyCode;
        if (code == 13) {
            tag = target.tagName;
            if (tag == "TEXTAREA") { return true; }
            else { return false; }
        }
    }
    else {
        target = event.target; //针对遵循w3c标准的浏览器，如Firefox
        code = event.keyCode;
        if (code == 13) {
            tag = target.tagName;
            if (tag == "INPUT") { return false; }
            else { return true; }
        }
    }
};

5.动端适配

(function (doc, win) {
    var docEl = doc.documentElement,
        resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
        recalc = function () {
            var clientWidth = docEl.clientWidth;
            var fontSize = 20;
            docEl.style.fontSize = fontSize + 'px';
            var docStyles = getComputedStyle(docEl);
            var realFontSize = parseFloat(docStyles.fontSize);
            var scale = realFontSize / fontSize;
            console.log("realFontSize: " + realFontSize + ", scale: " + scale);
            fontSize = clientWidth / 667 * 20;
            if(isIphoneX()) fontSize = 19;
            fontSize = fontSize / scale;
            docEl.style.fontSize = fontSize + 'px';
        };
    // Abort if browser does not support addEventListener
    if (!doc.addEventListener) return;
    win.addEventListener(resizeEvt, recalc, false);
    doc.addEventListener('DOMContentLoaded', recalc, false);

    // iphoneX判断
    function isIphoneX(){
        return /iphone/gi.test(navigator.userAgent) && (screen.height == 812 && screen.width == 375)
    }

})(document, window);

6.xss预防方式

// 敏感符号转义
function entities(s) {
    let e = {
        '"': '"',
        '&': '&',
        '<': '&lt;',
        '>': '&gt;'
    }
    return s.replace(/["<>&]/g, m => {
        return e[m]
    })
}

7.算法

/**
 * 节流函数--规定在一个单位时间内，只能触发一次函数。如果这个单位时间内触发多次函数，只有一次生效。
 */
function throttle(fun, delay) {
    let last, deferTimer
    return function (args) {
        let that = this
        let _args = arguments
        let now = +new Date()
        if (last && now < last + delay) {
            clearTimeout(deferTimer)
            deferTimer = setTimeout(function () {
                last = now
                fun.apply(that, _args)
            }, delay)
        }else {
            last = now
            fun.apply(that,_args)
        }
    }
}

/**
 * 防抖函数--在事件被触发n秒后再执行回调，如果在这n秒内又被触发，则重新计时
 */
 function debounce(fun, delay) {
    return function (args) {
        let that = this
        clearTimeout(fun.id)
        fun.id = setTimeout(function () {
            fun.call(that, args)
        }, delay)
    }
}

// 观察者模式
let Observer = (function(){
  let t __messages = {};
  return {
    regist: function(type, fn) {
      if(typeof __messages[type] === 'undefined') {
        messages[type] = [fn];
      }else {
        __messages[type].push(fn);
      }
    },
    fire: function(type, args) {
      if(!__messages[type]){
        return
      }
      let events = {
        type: type,
        args: args || {}
      },
      i = 0,
      len = __messages[type].length;
      for(;i<len;i++){
        __messages[type][i].call(this, events);
      }
    },
    remove: function(type, fn) {
      if(__messages[type] instanceof Array){
        let i = __messages[type].length -1;
        for(;i>=0;i--){
          __messages[type][i] === fn && __messages[type].splice(i, 1)
        }
      }
    }
  }
})();

 // 模板渲染方法
 function formatString(str, data) {
   return str.replace(/\{\{(\w+)\}\}/g, function(match, key) {
     return typeof data[key] === undefined ? '' : data[key]
   })
 }
 
 // 冒泡排序
function bubbleSort(arr) {
    for (let i = arr.length - 1; i > 0; i--) {
      for (let j = 0; j < i; j++) {
        if (arr[j] > arr[j + 1]) {
          swap(arr, j, j + 1);
        }
      }
    }
    return arr;
}

// 置换函数
function swap(arr, indexA, indexB) {
    [arr[indexA], arr[indexB]] = [arr[indexB], arr[indexA]];
}

// 数组去重
function distinct(arr = testArr) {
    return arr.filter((v, i, array) => array.indexOf(v) === i)
}

来源：公众号—趣谈前端