Detailed explanation of commonly used js reading and writing file sorting

Recently when writing js, I found that many rules are different from what I thought. After all, I just got started, so I took a lot of detours. Here is a summary and record. This article mainly shares with you the commonly used js reading and writing file sorting details. I hope it can Help everyone.

1, when the file tag is uploaded: the onchange method is no longer triggered when the same file is uploaded again
Method that wants to be triggered:

   $("#file").on("change", function (evt) {
        var fileExtend = fileName.substring(file.value.lastIndexOf('.'));
        //获取文件后缀  .zip/.png为了方便比较还可以把她转为小写.....
        this.value = '';
        //为了能持续触发onchange 因为当value值相同就不会再触发 特别是点击返回按钮过来的情况
    });

2, read the file information uploaded by file

$("#file").on("change", function () {
        var files = $(this).prop('files');        var reader = new FileReader();
        reader.readAsText(files[0], "UTF-8");//读取文件
        reader.onload = function (evt) {
            var fileString = evt.target.result; // 读取文件内容  
    }

3, generate local files

<a onfocus="this.blur();" style="display: none" id="createInvoteBtn" class="ipt-todo" href="javascript:void(0)">生成并导出Txt文件</a>
<a onfocus="this.blur();" style="display: none" id="createInvote" class="ipt-todo hide">code</a>

为了兼容IE请把上述标签写上,由于display:none所以不影响网页内容/**
*fileName  文件名
*fileData 需要写入文件的内容
*/
     function generateFile(fileName,fileData){          var isIE = (navigator.userAgent.indexOf(&#39;MSIE&#39;) >= 0);//是否是IE浏览器
            if (isIE) {                var winSave = window.open();
                winSave.document.open("text", "utf-8");
                winSave.document.write(fileData);
                winSave.document.execCommand("SaveAs", true, fileName);
                winSave.close();
            } else {                var mimeType = &#39;text/plain&#39;;
                $(&#39;#createInvote&#39;).attr(&#39;href&#39;, &#39;data:&#39; + mimeType + &#39;;charset=utf-8,&#39; + encodeURIComponent(fileData));                var btn = document.getElementById(&#39;createInvote&#39;);
                btn.download = fileName;
                document.getElementById(&#39;createInvote&#39;).click();//为了触发createInvote
            }
        }

4, sort map recursively according to the value of map(key, value) from major to small

/**
*map 是需要排序的对象
*newMap 排序后的map对象
*/

  var newMap = {};
 function orderMapByvalue(map) {        if (JSON.stringify(map) == "{}") {        //doSomething
            return newMap;//注意for(key in map)是异步遍历,所以对newMap的操作最好在return前
        }        for (key1 in map) {//只是为了获得第一组的key value 遍历一次就会break
            var tempKey = key1;            var tempValue = map[key1];            for (key2 in map) {                if (map[key2] - tempValue >= 0) {//这里是排序规则 根据需求改变
                    tempKey = key2;//接受value最大的key
                    tempValue = map[tempKey];//最大的value
                }
            }
           newMap[tempKey] =tempValue;//注意如果key是数字无论是你是什么时候插入 1还是"1" 系统会自动根据数字的大小重新排序,我这里的key不是纯数字,所以没问题
            delete map[tempKey];            break;//break是为了只for一次,毕竟js我没找到直接获取map第一个元素对的方法,只能这样来获取map里的第一组数据
        }
        orderMapByvalue(map);
    }

           

Recent When writing js, I found that many rules are different from what I thought. After all, I just got started, so I took a lot of detours. Here is a summary and record

1. When uploading with the file tag: the onchange method uploads the same file again. No longer being triggered
Methods that want to be triggered:

   $("#file").on("change", function (evt) {
        var fileExtend = fileName.substring(file.value.lastIndexOf('.'));//获取文件后缀  .zip/.png为了方便比较还可以把她转为小写.....
        this.value = '';//为了能持续触发onchange 因为当value值相同就不会再触发 特别是点击返回按钮过来的情况
    });

2, read the file information uploaded by file

$("#file").on("change", function () {
        var files = $(this).prop('files');        var reader = new FileReader();
        reader.readAsText(files[0], "UTF-8");//读取文件
        reader.onload = function (evt) {
            var fileString = evt.target.result; // 读取文件内容  
    }

3, generate local files

<a onfocus="this.blur();" style="display: none" id="createInvoteBtn" class="ipt-todo" href="javascript:void(0)">生成并导出Txt文件</a>
<a onfocus="this.blur();" style="display: none" id="createInvote" class="ipt-todo hide">code</a>

为了兼容IE请把上述标签写上,由于display:none所以不影响网页内容/**
*fileName  文件名
*fileData 需要写入文件的内容
*/
     function generateFile(fileName,fileData){          var isIE = (navigator.userAgent.indexOf(&#39;MSIE&#39;) >= 0);//是否是IE浏览器
            if (isIE) {                var winSave = window.open();
                winSave.document.open("text", "utf-8");
                winSave.document.write(fileData);
                winSave.document.execCommand("SaveAs", true, fileName);
                winSave.close();
            } else {                var mimeType = &#39;text/plain&#39;;
                $(&#39;#createInvote&#39;).attr(&#39;href&#39;, &#39;data:&#39; + mimeType + &#39;;charset=utf-8,&#39; + encodeURIComponent(fileData));                var btn = document.getElementById(&#39;createInvote&#39;);
                btn.download = fileName;
                document.getElementById(&#39;createInvote&#39;).click();//为了触发createInvote
            }
        }

4, Recursively sort map according to the value of map(key, value) from major to small

/**
*map 是需要排序的对象
*newMap 排序后的map对象
*/

  var newMap = {};
 function orderMapByvalue(map) {        if (JSON.stringify(map) == "{}") {        //doSomething
            return newMap;//注意for(key in map)是异步遍历,所以对newMap的操作最好在return前
        }        for (key1 in map) {//只是为了获得第一组的key value 遍历一次就会break
            var tempKey = key1;            var tempValue = map[key1];            for (key2 in map) {                if (map[key2] - tempValue >= 0) {//这里是排序规则 根据需求改变
                    tempKey = key2;//接受value最大的key
                    tempValue = map[tempKey];//最大的value
                }
            }
           newMap[tempKey] =tempValue;//注意如果key是数字无论是你是什么时候插入 1还是"1" 系统会自动根据数字的大小重新排序,我这里的key不是纯数字,所以没问题
            delete map[tempKey];            break;//break是为了只for一次,毕竟js我没找到直接获取map第一个元素对的方法,只能这样来获取map里的第一组数据
        }
        orderMapByvalue(map);
    }

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