无法覆盖 javascript 数组答案

【问题标题】：Can't overwrite javascript array无法覆盖 javascript 数组
【发布时间】：2022-02-16 20:01:41
【问题描述】：

我想跟踪“结果”的变化。如果 results.length 增加，数组将被覆盖并保存。如果长度减小，则数组将被覆盖，但新值不会保存。

playlists = [];
results = simpleMysqlQuery();
setinterval{
    update(playlists, results);
}

function update(playlists, results){
    if(playlists.length != results.length){
        playlists = reWritePlaylists(results, playlists);
    }
}

function reWritePlaylists(results, playlists){
   results.forEach(function(item, i, arr){
      playlists[i] = new Object();
      playlists[i]['id'] = results[i]['id'];
      playlists[i]['name'] = results[i]['name'];
   });
   if(playlists.length > results.length){
      playlists = playlists.slice(0, results.length);
   }
   return playlists;
}

【问题讨论】：

标签： javascript sql node.js arrays slice

【解决方案1】：

当你使用slice创建一个新数组时，新创建的数组不再是对原数组的引用，所以update中的playlists参数不再引用同一个数组实例playlists 函数外的变量。试试这个：

playlists = [];
results = simpleMysqlQuery();
setinterval{
    playlists = update(playlists, results);
}

function update(playlists, results){
    if(playlists.length != results.length){
        playlists = reWritePlaylists(results, playlists);
    }
    return playlists
}

function reWritePlaylists(results, playlists){
   results.forEach(function(item, i, arr){
      playlists[i] = new Object();
      playlists[i]['id'] = results[i]['id'];
      playlists[i]['name'] = results[i]['name'];
   });
   if(playlists.length > results.length){
      playlists = playlists.slice(0, results.length);
   }
   return playlists;
}

【讨论】：

没有帮助。数组现在根本不会被覆盖

【解决方案2】：

我找到了！

function reWritePlaylists(results, playlists){
   playlists.splice(0, playlists.length);
   results.forEach(function(item, i, arr){
      playlists[i] = new Object();
      playlists[i]['id'] = results[i]['id'];
      playlists[i]['name'] = results[i]['name'];
   });
   return playlists;
}

【讨论】：

【解决方案3】：

请更新 reWritePlaylists 函数如下：

function reWritePlaylists(results, playlists){
   playlists.splice(0, results.length);
   results.forEach(function(item, i, arr){
      playlists[i] = new Object();
      playlists[i]['id'] = results[i]['id'];
      playlists[i]['name'] = results[i]['name'];
   });
   return playlists;
}

【讨论】：

没有帮助。数组被覆盖但未保存。
只修改播放列表 = []; to playlists.splice(0, results.length);