Example analysis of javascript scope problem_javascript skills

During a recent project, I needed to generate a tree-like directory based on JSON data. The resulting code is as follows:

var folderList=[
  {
    "FolderName": "ASD",
    "ChildList": null
  },
  {
    "FolderName": "内网公告",
    "ChildList": null
  },
  {
    "FolderName": "测试文档",
    "ChildList": null
  },
  {
    "FolderName": "软件开发",
    "ChildList": null
  },
  {
    "FolderName": "Test",
    "ChildList": [
      {
        "FolderName": "Test2",
        "ChildList": [
          {
            "FolderName": "Test3",
            "ChildList": null
          }
        ]
      }
    ]
  },
  {
    "FolderName": "个人",
    "ChildList": null
  },
  {
    "FolderName": "公司通知",
    "ChildList": null
  },
  {
    "FolderName": "采购平台",
    "ChildList": null
  }
];
      var str='';
      function generateFolders(arr) {
        if (arr.length > 0) {
          str += '<div class="sui-list sui-list-icon ubt bc-gra1">';
          for (var i = 0, len = arr.length; i < len; i++) {
            str += '<ul class="ub ub-ac">' 
                + '<li class="sui-list-licon sui-icon-ok-circle fts2">' + '</li>' 
                + '<ul class="ub ub-f1 sui-list-item">' 
                 + '<li class="ub-f1 sui-list-text sui-list-nowrap">' + arr[i].FolderName + '</li>' 
                 + '<li class="sui-list-ricon ub-img sui-icon-chevron-right fts2"></li>' 
                + '</ul>' 
               + '</ul>';
            if (isDefine(arr[i].ChildList)) {
              str += generateFolders(arr[i].ChildList);
            }
          }
          str += '</div>';
          return str;
        }else{
          return '';
        }
      }

      var folderTxt ='<div class="sui-list sui-list-icon ubt bc-gra1">' 
                 +'<ul class="ub ub-ac">' 
                   +'<li class="sui-list-licon sui-icon-drawer fts2">' + '</li>' 
                   +'<ul class="ub ub-f1 sui-list-item">' 
                     +'<li class="ub-f1 sui-list-text sui-list-nowrap">我的目录</li>' 
                     +'<li class="sui-list-ricon ub-img sui-icon-chevron-right fts2"></li>' 
                   +'</ul>' 
                 +'</ul>';
      folderTxt+=generateFolders(folderList);
      folderTxt += '</div>';
      $('#list').html(folderTxt);
      /**
       * 判断是否是空
       * @param value
       */
      function isDefine(value){
        if(value == null || value == "" || value == "undefined" || value == undefined || value == "null" || value == "(null)" || value == 'NULL' || typeof(value) == 'undefined'){
          return false;
        }
        else{
       value = value+"";
          value = value.replace(/\s/g,"");
          if(value == ""){
            return false;
          }
          return true;
        }
      }

The resulting tree is as shown below:

After investigation, it was found that the problem was caused by the incorrect location of str definition. Just define str as a local variable.

function generateFolders(arr) {
        var str='';
        if (arr.length > 0) {
          str += '<div class="sui-list sui-list-icon ubt bc-gra1">';
          for (var i = 0, len = arr.length; i < len; i++) {
            str += '<ul class="ub ub-ac">' 
                + '<li class="sui-list-licon sui-icon-ok-circle fts2"></li>' 
                + '<ul class="ub ub-f1 sui-list-item">' 
                  + '<li class="ub-f1 sui-list-text sui-list-nowrap">' + arr[i].FolderName + '</li>' 
                  + '<li class="sui-list-ricon ub-img sui-icon-chevron-right fts2"></li>' 
                + '</ul>' 
              + '</ul>';
            if (isDefine(arr[i].ChildList)) {
              str += generateFolders(arr[i].ChildList);
            }
          }
          str += '</div>';
          return str;
        }else{
          return '';
        }
      }

After modification, the desired effect can be achieved:

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