JavaScript 开发常用工具函数精选

对象与数组操作

处理数据转换、克隆和去重是日常高频需求。注意深拷贝的局限性及类数组的判断标准。

// 属性混合
function extend(to, _from) {
    for(let key in _from) {
        to[key] = _from[key];
    }
    return to
}

// 浅拷贝实现
Object.assign = Object.assign || function(){
    if(arguments.length === 0) throw new TypeError('Cannot convert undefined or null to object');
    
    let target = arguments[0],
        args = Array.prototype.slice.call(arguments, 1),
        key
    args.forEach(function(item){
        for(key in item){
            item.hasOwnProperty(key) && ( target[key] = item[key] )
        }
    })
    return target
}

// 简单深拷贝（JSON 方案）
let clone = JSON.parse(JSON.stringify(target))

// 通用克隆（支持深度）
function clone(value, deep) {
    if (isPrimitive(value)) {
        return value
    }

    if (isArrayLike(value)) {
        value = Array.prototype.slice.call(value)
        return deep ? value.map(item => clone(item, deep)) : value
    } else if (isPlainObject(value)) {
        let target = {}, key;
        for (key in value) {
            value.hasOwnProperty(key) && (target[key] = deep ? clone(value[key], deep) : value[key])
        }
        return target
    }

    let type = getRawType(value)
    switch (type) {
        case 'Date':
        case 'RegExp':
        case 'Error': value = new window[type](value); break;
    }
    return value
}

// 检查是否为有效长度
function isLength(value) {
    return typeof value == 'number' && value > -1 && value % 1 == 0 && value <= Number.MAX_SAFE_INTEGER;
}

// 检查类数组
function isArrayLike(value) {
    return value != null && isLength(value.length) && !isFunction(value);
}

// 检查是否为空
function isEmpty(value) {
    if (value == null) {
        return true;
    }
    if (isArrayLike(value)) {
        return !value.length;
    } else if (isPlainObject(value)) {
        for (let key in value) {
            if (hasOwnProperty.call(value, key)) {
                return false;
            }
        }
        return true;
    }
    return false;
}

// 记忆化函数缓存结果
function cached(fn) {
    let cache = Object.create(null);
    return function cachedFn(str) {
        let hit = cache[str];
        return hit || (cache[str] = fn(str))
    }
}

// 数组去重
function unique(arr) {
    if (!isArrayLike(arr)) {
        return arr
    }
    let result = []
    let objarr = []
    let obj = Object.create(null)
    
    arr.forEach(item => {
        if (isStatic(item)) {
            let key = item + '_' + getRawType(item);
            if (!obj[key]) {
                obj[key] = true
                result.push(item)
            }
        } else {
            if (objarr.indexOf(item) === -1) {
                objarr.push(item)
                result.push(item)
            }
        }
    })
    return result
}

// Set 简易实现
window.Set = window.Set || (function () {
    function Set(arr) {
        this.items = arr ? unique(arr) : [];
        this.size = this.items.length;
    }
    Set.prototype = {
        add: function (value) {
            if (!this.has(value)) {
                this.items.push(value);
                this.size++;
            }
            return this;
        },
        clear: function () {
            this.items = []
            this.size = 0
        },
        delete: function (value) {
            return this.items.some((v, i) => {
                if (v === value) {
                    this.items.splice(i, 1)
                    return true
                }
                return false
            })
        },
        has: function (value) {
            return this.items.some(v => v === value)
        },
        values: function () {
            return this.items
        },
    }
    return Set;
}());

// 数值运算
function max(arr) {
    arr = arr.filter(item => !_isNaN(item))
    return arr.length ? Math.max.apply(null, arr) : undefined
}

function min(arr) {
    arr = arr.filter(item => !_isNaN(item))
    return arr.length ? Math.min.apply(null, arr) : undefined
}

function random(lower, upper) {
    lower = +lower || 0
    upper = +upper || 0
    return Math.random() * (upper - lower) + lower;
}

字符串与格式化

处理命名规范转换和时间格式化时，正则表达式配合记忆化缓存效果最佳。

// 横线转驼峰
let camelizeRE = /-(\w)/g;
function camelize(str) {
    return str.replace(camelizeRE, function(_, c) {
        return c ? c.toUpperCase() : '';
    })
}
let _camelize = cached(camelize)

// 驼峰转横线
let hyphenateRE = /\B([A-Z])/g;
function hyphenate(str) {
    return str.replace(hyphenateRE, '-$1').toLowerCase()
}
let _hyphenate = cached(hyphenate);

// 首字母大写
function capitalize(str) {
    return str.charAt(0).toUpperCase() + str.slice(1)
}
let _capitalize = cached(capitalize)

// 生成重复字符串
function repeat(str, n) {
    let res = '';
    while(n) {
        if(n % 2 === 1) {
            res += str;
        }
        if(n > 1) {
            str += str;
        }
        n >>= 1;
    }
    return res
};

// 时间格式化
function dateFormater(formater, t) {
    let date = t ? new Date(t) : new Date(),
        Y = date.getFullYear() + '',
        M = date.getMonth() + 1,
        D = date.getDate(),
        H = date.getHours(),
        m = date.getMinutes(),
        s = date.getSeconds();
    return formater.replace(/YYYY|yyyy/g, Y)
        .replace(/YY|yy/g, Y.substr(2, 2))
        .replace(/MM/g, (M < 10 ? '0' : '') + M)
        .replace(/DD/g, (D < 10 ? '0' : '') + D)
        .replace(/HH|hh/g, (H < 10 ? '0' : '') + H)
        .replace(/mm/g, (m < 10 ? '0' : '') + m)
        .replace(/ss/g, (s < 10 ? '0' : '') + s)
}

// 时间格式转换
function dateStrForma(str, from, to) {
    str += ''
    let Y = ''
    if (~(Y = from.indexOf('YYYY'))) {
        Y = str.substr(Y, 4)
        to = to.replace(/YYYY|yyyy/g, Y)
    } else if (~(Y = from.indexOf('YY'))) {
        Y = str.substr(Y, 2)
        to = to.replace(/YY|yy/g, Y)
    }

    let k, i
    ['M', 'D', 'H', 'h', 'm', 's'].forEach(s => {
        i = from.indexOf(s + s)
        k = ~i ? str.substr(i, 2) : ''
        to = to.replace(s + s, k)
    })
    return to
}

环境与浏览器检测

针对不同运行环境和浏览器特性进行适配，是前端工程化的重要一环。

// 基础环境判断
let inBrowser = typeof window !== 'undefined';
let inWeex = typeof WXEnvironment !== 'undefined' && !!WXEnvironment.platform;
let weexPlatform = inWeex && WXEnvironment.platform.toLowerCase();
let UA = inBrowser && window.navigator.userAgent.toLowerCase();
let isIE = UA && /msie|trident/.test(UA);
let isIE9 = UA && UA.indexOf('msie 9.0') > 0;
let isEdge = UA && UA.indexOf('edge/') > 0;
let isAndroid = (UA && UA.indexOf('android') > 0) || (weexPlatform === 'android');
let isIOS = (UA && /iphone|ipad|ipod|ios/.test(UA)) || (weexPlatform === 'ios');
let isChrome = UA && /chrome/\d+/.test(UA) && !isEdge;

// 获取浏览器详细信息
function getExplorerInfo() {
    let t = navigator.userAgent.toLowerCase();
    return 0 <= t.indexOf("msie") ? { 
        type: "IE",
        version: Number(t.match(/msie ([\d]+)/)[1])
    } : !!t.match(/trident/.+?rv:(([\d.]+))/) ? { 
        type: "IE",
        version: 11
    } : 0 <= t.indexOf("edge") ? {
        type: "Edge",
        version: Number(t.match(/edge\/([\d]+)/)[1])
    } : 0 <= t.indexOf("firefox") ? {
        type: "Firefox",
        version: Number(t.match(/firefox\/([\d]+)/)[1])
    } : 0 <= t.indexOf("chrome") ? {
        type: "Chrome",
        version: Number(t.match(/chrome\/([\d]+)/)[1])
    } : 0 <= t.indexOf("opera") ? {
        type: "Opera",
        version: Number(t.match(/opera.([\d]+)/)[1])
    } : 0 <= t.indexOf("Safari") ? {
        type: "Safari",
        version: Number(t.match(/version\/([\d]+)/)[1])
    } : {
        type: t,
        version: -1
    }
}

// PC 端检测
function isPCBroswer() {
    let e = navigator.userAgent.toLowerCase()
        , t = "ipad" == e.match(/ipad/i)
        , i = "iphone" == e.match(/iphone/i)
        , r = "midp" == e.match(/midp/i)
        , n = "rv:1.2.3.4" == e.match(/rv:1.2.3.4/i)
        , a = "ucweb" == e.match(/ucweb/i)
        , o = "android" == e.match(/android/i)
        , s = "windows ce" == e.match(/windows ce/i)
        , l = "windows mobile" == e.match(/windows mobile/i);
    return !(t || i || r || n || a || o || s || l)
}

// 判断是否为内置函数
function isNative(value) {
    return typeof value === 'function' && /[native code]/.test(value.toString())
}

DOM 与性能优化

涉及文件下载、全屏控制及页面性能分析的工具函数。

// URL 参数解析
function GetUrlParam() {
    let url = document.location.toString();
    let arrObj = url.split("?");
    let params = Object.create(null)
    if (arrObj.length > 1) {
        arrObj = arrObj[1].split("&");
        arrObj.forEach(item => {
            item = item.split("=");
            params[item[0]] = item[1] || ''
        })
    }
    return params;
}

// Base64 文件下载
function downloadFile(filename, data) {
    let DownloadLink = document.createElement('a');
    if (DownloadLink) {
        document.body.appendChild(DownloadLink);
        DownloadLink.style = 'display: none';
        DownloadLink.download = filename;
        DownloadLink.href = data;
        if (document.createEvent) {
            let DownloadEvt = document.createEvent('MouseEvents');
            DownloadEvt.initEvent('click', true, false);
            DownloadLink.dispatchEvent(DownloadEvt);
        } else if (document.createEventObject) {
            DownloadLink.fireEvent('onclick');
        } else if (typeof DownloadLink.onclick == 'function') {
            DownloadLink.onclick();
        }
        document.body.removeChild(DownloadLink);
    }
}

// 全屏控制
function toFullScreen() {
    let el = document.documentElement;
    let rfs = el.requestFullScreen || el.webkitRequestFullScreen || el.mozRequestFullScreen || el.msRequestFullScreen;
    if (rfs) {
        rfs.call(el);
    } else if (typeof window.ActiveXObject !== "undefined") {
        let wscript = new ActiveXObject("WScript.Shell");
        if (wscript != null) {
            wscript.SendKeys("{F11}");
        }
    } else {
        alert("浏览器不支持全屏");
    }
}

function exitFullscreen() {
    let el = document.documentElement;
    let cfs = el.cancelFullScreen || el.webkitCancelFullScreen || el.mozCancelFullScreen || el.exitFullScreen;
    if (cfs) {
        cfs.call(el);
    } else if (typeof window.ActiveXObject !== "undefined") {
        let wscript = new ActiveXObject("WScript.Shell");
        if (wscript != null) {
            wscript.SendKeys("{F11}");
        }
    } else {
        alert("切换失败，可尝试 Esc 退出");
    }
}

// 动画帧控制
window.requestAnimationFrame = window.requestAnimationFrame ||
    window.webkitRequestAnimationFrame ||
    window.mozRequestAnimationFrame ||
    window.msRequestAnimationFrame ||
    window.oRequestAnimationFrame ||
    function (callback) {
        window.setTimeout(callback, 1000 / 60);
    };

window.cancelAnimationFrame = window.cancelAnimationFrame ||
    window.webkitCancelAnimationFrame ||
    window.mozCancelAnimationFrame ||
    window.msCancelAnimationFrame ||
    window.oCancelAnimationFrame ||
    function (id) {
        window.clearTimeout(id);
    }

// 性能分析
window.onload = function () {
    setTimeout(function () {
        let t = performance.timing
        console.log('DNS 查询耗时：' + (t.domainLookupEnd - t.domainLookupStart).toFixed(0))
        console.log('TCP 链接耗时：' + (t.connectEnd - t.connectStart).toFixed(0))
        console.log('request 请求耗时：' + (t.responseEnd - t.responseStart).toFixed(0))
        console.log('解析 dom 树耗时：' + (t.domComplete - t.domInteractive).toFixed(0))
        console.log('白屏时间：' + (t.responseStart - t.navigationStart).toFixed(0))
        console.log('domready 时间：' + (t.domContentLoadedEventEnd - t.navigationStart).toFixed(0))
        console.log('onload 时间：' + (t.loadEventEnd - t.navigationStart).toFixed(0))

        if (performance.memory) {
            console.log('js 内存使用占比：' + (performance.memory.usedJSHeapSize / performance.memory.totalJSHeapSize * 100).toFixed(2) + '%')
        }
    })
}

// 键盘事件拦截
document.addEventListener('keydown', function (event) {
    return !(
        112 == event.keyCode || // F1
        123 == event.keyCode || // F12
        event.ctrlKey && 82 == event.keyCode || // ctrl + R
        event.ctrlKey && 78 == event.keyCode || // ctrl + N
        event.shiftKey && 121 == event.keyCode || // shift + F10
        event.altKey && 115 == event.keyCode || // alt + F4
        "A" == event.target.tagName && event.shiftKey // shift + 点击 a 标签
    ) || (event.returnValue = false)
});

// 禁止右键、选择、复制
['contextmenu', 'selectstart', 'copy'].forEach(function (ev) {
    document.addEventListener(ev, function (event) {
        return event.returnValue = false
    });
});

原生方法补全

为了兼容旧环境，部分常用 API 提供了 Polyfill 实现。

// 非 NaN 检查
function _isNaN(v) {
    return !(typeof v === 'string' || typeof v === 'number') || isNaN(v)
}

// Object.keys/values
Object.keys = Object.keys || function keys(object) {
    if (object === null || object === undefined) {
        throw new TypeError('Cannot convert undefined or null to object');
    }
    let result = []
    if (isArrayLike(object) || isPlainObject(object)) {
        for (let key in object) {
            object.hasOwnProperty(key) && (result.push(key))
        }
    }
    return result
}

Object.values = Object.values || function values(object) {
    if (object === null || object === undefined) {
        throw new TypeError('Cannot convert undefined or null to object');
    }
    let result = []
    if (isArrayLike(object) || isPlainObject(object)) {
        for (let key in object) {
            object.hasOwnProperty(key) && (result.push(object[key]))
        }
    }
    return result
}

// Array.fill
Array.prototype.fill = Array.prototype.fill || function fill(value, start, end) {
    let ctx = this
    let length = ctx.length;
    start = parseInt(start)
    if (isNaN(start)) {
        start = 0
    } else if (start < 0) {
        start = -start > length ? 0 : (length + start);
    }
    end = parseInt(end)
    if (isNaN(end) || end > length) {
        end = length
    } else if (end < 0) {
        end += length;
    }
    while (start < end) {
        ctx[start++] = value;
    }
    return ctx;
}

// Array.includes
Array.prototype.includes = Array.prototype.includes || function includes(value, start) {
    let ctx = this
    let length = ctx.length;
    start = parseInt(start)
    if (isNaN(start)) {
        start = 0
    } else if (start < 0) {
        start = -start > length ? 0 : (length + start);
    }
    let index = ctx.indexOf(value)
    return index >= start;
}

// Array.find
Array.prototype.find = Array.prototype.find || function find(fn, ctx) {
    fn = fn.bind(ctx)
    let result;
    this.some((value, index, arr) => {
        return fn(value, index, arr) ? (result = value, true) : false
    })
    return result
}

// Array.findIndex
Array.prototype.findIndex = Array.prototype.findIndex || function findIndex(fn, ctx) {
    fn = fn.bind(ctx)
    let result;
    this.some((value, index, arr) => {
        return fn(value, index, arr) ? (result = index, true) : false
    })
    return result
}

// 根据路径获取属性
function getPropByPath(obj, path, strict) {
    let tempObj = obj;
    path = path.replace(/\[(\w+)\]/g, '.$1');
    path = path.replace(/^\./, '');
    let keyArr = path.split('.');
    let i = 0;
    for (let len = keyArr.length; i < len - 1; ++i) {
        if (!tempObj && !strict) break;
        let key = keyArr[i];
        if (key in tempObj) {
            tempObj = tempObj[key];
        } else {
            if (strict) {
                throw new Error('please transfer a valid prop path to form item!');
            }
            break;
        }
    }
    return {
        o: tempObj,
        k: keyArr[i],
        v: tempObj ? tempObj[keyArr[i]] : null
    };
}