Summarize the JS functions commonly used in front-end development (2)-JS Tutorial-php.cn

25、unique：数组去重，返回一个新数组

function unique(arr){
    if(!isArrayLink(arr)){ //不是类数组对象
        return arr
    }
    let result = []
    let objarr = []
    let obj = Object.create(null)
    
    arr.forEach(item => {
        if(isStatic(item)){//是除了symbol外的原始数据
            let key = item + '_' + getRawType(item);
            if(!obj[key]){
                obj[key] = true
                result.push(item)
            }
        }else{//引用类型及symbol
            if(!objarr.includes(item)){
                objarr.push(item)
                result.push(item)
            }
        }
    })
    
    return resulte
}

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26、Set简单实现

window.Set = window.Set || (function () {
    function Set(arr) {
        this.items = arr ? unique(arr) : [];
        this.size = this.items.length; // Array的大小
    }
    Set.prototype = {
        add: function (value) {
            // 添加元素,若元素已存在,则跳过，返回 Set 结构本身。
            if (!this.has(value)) {
                this.items.push(value);
                this.size++;
            }
            return this;
        },
        clear: function () {
            //清除所有成员，没有返回值。
            this.items = []
            this.size = 0
        },
        delete: function (value) {
            //删除某个值，返回一个布尔值，表示删除是否成功。
            return this.items.some((v, i) => {
                if(v === value){
                    this.items.splice(i,1)
                    return true
                }
                return false
            })
        },
        has: function (value) {
            //返回一个布尔值，表示该值是否为Set的成员。
            return this.items.some(v => v === value)
        },
        values: function () {
            return this.items
        },
    }

    return Set;
}());

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27、repeat：生成一个重复的字符串，有n个str组成，可修改为填充为数组等

function repeat(str, n) {
    let res = '';
    while(n) {
        if(n % 2 === 1) {
            res += str;
        }
        if(n > 1) {
            str += str;
        }
        n >>= 1;
    }
    return res
};
//repeat('123',3) ==> 123123123

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28、dateFormater：格式化时间

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)
}
// dateFormater('YYYY-MM-DD HH:mm', t) ==> 2019-06-26 18:30
// dateFormater('YYYYMMDDHHmm', t) ==> 201906261830

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29、dateStrForma：将指定字符串由一种时间格式转化为另一种。From的格式应对应str的位置

function dateStrForma(str, from, to){
    //'20190626' 'YYYYMMDD' 'YYYY年MM月DD日'
    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
}
// dateStrForma('20190626', 'YYYYMMDD', 'YYYY年MM月DD日') ==> 2019年06月26日
// dateStrForma('121220190626', '----YYYYMMDD', 'YYYY年MM月DD日') ==> 2019年06月26日
// dateStrForma('2019年06月26日', 'YYYY年MM月DD日', 'YYYYMMDD') ==> 20190626

// 一般的也可以使用正则来实现
//'2019年06月26日'.replace(/(\d{4})年(\d{2})月(\d{2})日/, '$1-$2-$3') ==> 2019-06-26

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30、getPropByPath：根据字符串路径获取对象属性：‘obj[0].count’

function getPropByPath(obj, path, strict) {
      let tempObj = obj;
      path = path.replace(/\[(\w+)\]/g, '.$1'); //将[0]转化为.0
      path = path.replace(/^\./, ''); //去除开头的.

      let keyArr = path.split('.'); //根据.切割
      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) {//开启严格模式，没找到对应key值，抛出错误
                throw new Error('please transfer a valid prop path to form item!');
            }
            break;
        }
      }
      return {
        o: tempObj, //原始数据
        k: keyArr[i], //key值
        v: tempObj ? tempObj[keyArr[i]] : null // key值对应的值
      };
};

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31、GetUrlParam：获取Url参数，返回一个对象

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;
}
// ?a=1&b=2&c=3 ==> {a: "1", b: "2", c: "3"}

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32、downloadFile：base64数据导出文件，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);
	}
}

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33、toFullScreen：全屏

function toFullScreen() {
	let elem = document.body;
    elem.webkitRequestFullScreen
    ? elem.webkitRequestFullScreen()
    : elem.mozRequestFullScreen
    ? elem.mozRequestFullScreen()
    : elem.msRequestFullscreen
    ? elem.msRequestFullscreen()
    : elem.requestFullScreen
    ? elem.requestFullScreen()
    : alert("浏览器不支持全屏");
}

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34、exitFullscreen：退出全屏

function exitFullscreen() {
	let elem = parent.document;
	elem.webkitCancelFullScreen
	? elem.webkitCancelFullScreen()
	: elem.mozCancelFullScreen
	? elem.mozCancelFullScreen()
    : elem.cancelFullScreen
    ? elem.cancelFullScreen()
    : elem.msExitFullscreen
    ? elem.msExitFullscreen()
    : elem.exitFullscreen
    ? elem.exitFullscreen()
    : alert("切换失败,可尝试Esc退出");
}

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35、requestAnimationFrame：window动画

window.requestAnimationFrame = window.requestAnimationFrame ||
	window.webkitRequestAnimationFrame ||
    window.mozRequestAnimationFrame ||
    window.msRequestAnimationFrame ||
    window.oRequestAnimationFrame ||
    function (callback) {
		//为了使setTimteout的尽可能的接近每秒60帧的效果
		window.setTimeout(callback, 1000 / 60);
	}
window.cancelAnimationFrame = window.cancelAnimationFrame ||
	window.webkitCancelAnimationFrame ||
    window.mozCancelAnimationFrame ||
    window.msCancelAnimationFrame ||
    window.oCancelAnimationFrame ||
    function (id) {
		//为了使setTimteout的尽可能的接近每秒60帧的效果
        window.clearTimeout(id);
	}

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36、_isNaN：检查数据是否是非数字值

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

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37、max：求取数组中非NaN数据中的最大值

function max(arr){
    arr = arr.filter(item => !_isNaN(item))
    return arr.length ? Math.max.apply(null, arr) : undefined
}
//max([1, 2, '11', null, 'fdf', []]) ==> 11

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38、min：求取数组中非NaN数据中的最小值

function min(arr){
    arr = arr.filter(item => !_isNaN(item))
    return arr.length ? Math.min.apply(null, arr) : undefined
}
//min([1, 2, '11', null, 'fdf', []]) ==> 1

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39、random：返回一个lower-upper直接的随机数。（lower、upper无论正负与大小，但必须是非NaN的数据）

function random(lower, upper) {
	lower = +lower || 0
	upper = +upper || 0
	return Math.random() * (upper - lower) + lower;
}
//random(0, 0.5) ==> 0.3567039135734613
//random(2, 1) ===> 1.6718418553475423
//random(-2, -1) ==> -1.4474325452361945

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40、Object.keys:返回一个由一个给定对象的自身可枚举属性组成的数组

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;
}

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41、Object.values:返回一个给定对象自身的所有可枚举属性值的数组

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;
}

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42、arr.fill:使用value值填充array，从start位置开始，到end位置结束（但不包含end位置），返回原数组

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(3).fill(2) ===> [2, 2, 2]

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43、arr.includes:用来判断一个数组是否包含一个指定的值，如果是返回true，否则返回false，可指定开始查询的位置

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;
}

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44、返回数组中通过测试（函数fn内判断）的第一个元素的值

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

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45、arr.findIndex:返回数组中通过测试（函数fn内判断）的第一个元素的下标

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

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46、performance.timing:利用performance.timing进行性能分析

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 (t = performance.memory) {
			console.log('js内存使用占比：' +  (t.usedJSHeapSize / t.totalJSHeapSize * 100).toFixed(2) + '%')
		}
	})
}

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47、禁止某些键盘事件

document.addEventListener('keydown', function(event) {
	return !(
		112 == event.keyCode ||		//禁止F1
		123 == event.keyCode ||		//禁止F12
		event.ctrlKey && 82 == event.keyCode ||		//禁止ctrl+R
		event.ctrlKey && 18 == event.keyCode ||		//禁止ctrl+N
		event.shiftKey && 121 == event.keyCode ||  		//禁止shift+F10
		event.altKey && 115 == event.keyCode ||		//禁止alt+F4
		"A" == event.srcElement.tagName && event.shiftKey		//禁止shift+点击a标签
	) || （event.returnValue = false）
});

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48、禁止右键、选择、复制

['contextmenu', 'selectstart', 'copy'].forEach(function(ev) {
	document.addEventListener(ev, function(event) {
		return event.returnValue = false;
	})
});

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以上两篇文章就是整理的48个前端开发常用函数，欢迎大家继续补充。谢谢！

更多JavaScript相关内容请访问PHP中文网：//m.sbmmt.com/

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