开发中常用的JS知识点集锦

//深拷贝函数（满足属性多级嵌套）
function deepCloneObj(sourceObj){
    var obj = (sourceObj instanceof Array) ? [] : {};
    
    for (var key in sourceObj){
        var tmp = sourceObj[key];
        
        //处理重复引用，防止死循环
        if (tmp === sourceObj){
            continue; 
        }

        if (typeof tmp === 'object'){
            obj[key] = arguments.callee(tmp); //属性为对象，递归深度复制
        }
        else{
            obj[key] = tmp;
        }
    }
    return obj;
}

//1、测试对象的深拷贝
var obj = {info:{name:'大锤'}, sign: 'xxx'};
var obj2 = Object.assign({}, obj);  //一级属性深拷贝 （es6的Object.assign函数特性）
var obj3 = {...obj};            //一级属性深拷贝 (es6扩展运算符)
var obj4 =  deepCloneObj(obj);  //递归深拷贝所有层级属性
var obj5 = JSON.parse(JSON.stringify(obj)); //深拷贝所有层级属性

console.log('obj: ', JSON.stringify(obj));
console.log('obj2: ', JSON.stringify(obj2));
console.log('obj3: ', JSON.stringify(obj3));
console.log('obj4: ', JSON.stringify(obj4));
console.log('obj5: ', JSON.stringify(obj5));
console.log(".........end..........");

setTimeout(function(){

    obj.sign = 'a**b'; 
    obj.info.name = '一二三';
    console.log('\n****update info ****');
    console.log('obj: ', JSON.stringify(obj));
    console.log('obj2: ', JSON.stringify(obj2));
    console.log('obj3: ', JSON.stringify(obj3));
    console.log('obj4: ', JSON.stringify(obj4));
    console.log('obj5: ', JSON.stringify(obj5));
    console.log(".........end..........");
},100);

/*
打印日志结果：
obj:  {"info":{"name":"大锤"},"sign":"xxx"}
obj2:  {"info":{"name":"大锤"},"sign":"xxx"}
obj3:  {"info":{"name":"大锤"},"sign":"xxx"}
obj4:  {"info":{"name":"大锤"},"sign":"xxx"}
obj5:  {"info":{"name":"大锤"},"sign":"xxx"}
.........end..........

****update info ****
obj:  {"info":{"name":"一二三"},"sign":"a**b"}   //只拷贝了第一级属性
obj2:  {"info":{"name":"一二三"},"sign":"xxx"}   //只拷贝了第一级属性
obj3:  {"info":{"name":"一二三"},"sign":"xxx"}   //只拷贝了第一级属性
obj4:  {"info":{"name":"大锤"},"sign":"xxx"}     //所有层级深拷贝
obj5:  {"info":{"name":"大锤"},"sign":"xxx"}    //所有层级深拷贝

*/


//2、测试数组的深拷贝
setTimeout(function(){
    console.log('\n\n.....数组的深拷贝测试....');
    var arr = [{name: '小明'}, true, 18];
    var arr2 = Object.assign([], arr);
    var arr3 = [...arr2];
    var arr4 = deepCloneObj(arr);
    var arr5 = JSON.parse(JSON.stringify(arr));

    console.log('arr: ', JSON.stringify(arr));
    console.log('arr2: ', JSON.stringify(arr2));
    console.log('arr3: ', JSON.stringify(arr3));
    console.log('arr4: ', JSON.stringify(arr4));
    console.log('arr5: ', JSON.stringify(arr5));
    console.log("......end......\n");

    setTimeout(function(){

        arr[0].name = '五六七', arr[1] = false, arr[2] = 99;
        console.log('arr: ', JSON.stringify(arr));
        console.log('arr2: ', JSON.stringify(arr2));
        console.log('arr3: ', JSON.stringify(arr3));
        console.log('arr4: ', JSON.stringify(arr4));
        console.log('arr5: ', JSON.stringify(arr5));

    }, 100);
    
    /*
    数组测试打印日志结果：
    .....数组的深拷贝测试....
    arr:  [{"name":"小明"},true,18]
    arr2:  [{"name":"小明"},true,18]
    arr3:  [{"name":"小明"},true,18]
    arr4:  [{"name":"小明"},true,18]
    arr5:  [{"name":"小明"},true,18]
    ......end......

    arr:  [{"name":"五六七"},false,99]
    arr2:  [{"name":"五六七"},true,18]    //只拷贝了第一级属性
    arr3:  [{"name":"五六七"},true,18]   //只拷贝了第一级属性
    arr4:  [{"name":"小明"},true,18]    //所有层级深拷贝
    arr5:  [{"name":"小明"},true,18]   //所有层级深拷贝
    */

},1000);

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                 * 根据远程图片转成base64数据 (远程图片和当前页面不是同一域名时，需要进行web服务器配置，使其可以跨域下载)
                 * @param url      图片链接
                 * @param callback 回调函数
                 */
                function getBase64ByImgUrl(url, callback){
                    let canvas = document.createElement('canvas'),
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                    img.onload = function(){
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                        canvas.width = img.width;
                        ctx.drawImage(img,0,0);

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                        let base64 = canvas.toDataURL('image/png');
                        //回调
                        if (callback){
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                        canvas = null;
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                    img.src = url;
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                /**
                 * 把base64转成文件流
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                 */
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                    let arr = base64.split(','), mime = arr[0].match(/:(.*?);/)[1],
                        bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);

                    while(n--){
                        u8arr[n] = bstr.charCodeAt(n);
                    }

                    return new File([u8arr], filename, {type:mime});
                }


                /**
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                 */
                function clickMeDownload(){

                    let imgUrl = 'https://img2018.cnblogs.com/blog/454511/201811/454511-20181114115022054-611805083.png';

                    getBase64ByImgUrl(imgUrl, function(base64){
                        console.log(base64);

                        //创建a标签, 设置a标签的href属性和download属性
                        var aEle = document.createElement('a');
                        aEle.setAttribute('href', base64);
                        aEle.setAttribute('download', 'temp.png');
                        aEle.style.display = 'none'; //隐藏a标签
                        document.body.appendChild(aEle);  //将a标签添加到body里
                        aEle.click();    //触发a标签点击事件

                        document.body.removeChild(aEle);  //下载图片后，移除a标签

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