Question

你能帮助我吗？当我运行它时，我在'bindTaskEvents'函数中得到“未捕获的TypeError：无法读取未定义的属性'querySelector'，其中该函数处理”completedTasksHolder“列表。在控制台中尝试这个：

console.log(completedTasksHolder.children[0])

返回唯一的李就好了。

var taskInput = document.getElementById("new-task"); // new-task
var addButton = document.getElementsByTagName("button")[0]; // first button
var incompleteTasksHolder = document.getElementById("incomplete-tasks"); // ul#incomplete-tasks
var completedTasksHolder = document.getElementById("completed-tasks"); // ul#completed-tasks

// Add a new task
var addTask = function(){
    console.log("Add task...");
}
// Edit an existing task
var editTask = function() {
    console.log("Edit task...");
}

var deleteTask = function() {
    console.log("Delete task...");
// Delete an existing task

    // When the Delete button is pressed
        // Remove the parent li from the ul
}

var taskCompleted = function() {
    console.log("Complete task...");
// Mark a task as complete
    // When the checkbox is checked
        // Append the task li to the #completed-tasks
}

// Mark a task as incomplete
var taskIncomplete = function() {
    console.log("Incomplete task...");
    // When the checkbox is unchecked
        // Append the task li to the #incomplete-tasks
}

var bindTaskEvents = function(taskListItem, checkBoxEventHandler) {
    console.log("Bind li events");
    // select li's children
    var checkbox = taskListItem.querySelector("input[type=checkbox]");
    var editButton = taskListItem.querySelector("button.edit");
    var deleteButton = taskListItem.querySelector("button.delete");

    // bind editTask to editButton
    editButton.onclick = editTask;

    //  bind deleteTask to deleteButton;
    deleteButton.onclick = deleteTask;

    // bind checkBoxEventHandler to checkbox
    checkbox.onchange = checkBoxEventHandler;
}

// Set the click handler to the addTask function
addButton.onclick = addTask;

// Cycle over incompleteTasksHiolder ul list items
for (var i = 0; incompleteTasksHolder.children.length; i++) {
        // bind events to li' children (taskCompleted)
    bindTaskEvents(incompleteTasksHolder.children[i], taskCompleted);
}     

// Cycle over completedTasksHiolder ul list items

for (var i = 0; completedTasksHolder.children.length; i++) {
        // bind events to li' children (taskCompleted)
    bindTaskEvents(completedTasksHolder.children[i], taskIncomplete);
}

这里有什么不对？谢谢！

Answer 1

问题在于for循环

替换

for (var i = 0; incompleteTasksHolder.children.length; i++) {

与

for (var i = 0; i < incompleteTasksHolder.children.length; i++) {

，同样适用于completedTasksHolder

基本上你创建了一个没有结束条件的循环，在某些时候incompleteTasksHolder.children[i]是undefined。

Answer 2

＆＃13;

var db = null;
var db2 = null;
var db3 = null;
var dbUser = null;
var dbName = "estudos.db";

var app = {
    // Application Constructor
    initialize: function() {
        document.addEventListener('deviceready', this.onDeviceReady.bind(this), false);
    },

    // deviceready Event Handler
    //
    // Bind any cordova events here. Common events are:
    // 'pause', 'resume', etc.
    onDeviceReady: function() {
        this.receivedEvent('deviceready');
    },

    // Update DOM on a Received Event
    receivedEvent: function(id) {
        var parentElement = document.getElementById(id);
        var listeningElement = parentElement.querySelector('.listening');
        var receivedElement = parentElement.querySelector('.received');

        listeningElement.setAttribute('style', 'display:none;');
        receivedElement.setAttribute('style', 'display:block;');


        // OPERACOES BD - inicio

        //banco de dados local - aceite de termos e outras coisas
        dbUser = window.sqlitePlugin.openDatabase({name: 'user.db', location: 'default'});
        dbUser.transaction(function(tx) {
            tx.executeSql('CREATE TABLE IF NOT EXISTS Users (flg_aceite, flg_valid_bd)');
        }, function(error) {
            alert('Transaction ERROR: ' + error.message);
        }, function() {
            console.log('Database OK');
        });

        //copia do banco de dados de estudos
        window.plugins.sqlDB.copy(dbName, 0, copysuccess, copyerror);
        // OPERACOES BD - fim
    }
};

app.initialize();

//---------------------------------------------------------------

function copysuccess()
{
    //primeira versão deste banco de dados. o comando anterior.
    //provavelmente realizou a cópia, abro o BD.
    db = window.sqlitePlugin.openDatabase({name: dbName});
    //preciso verificar se existem versões anteriores deste BD. Deleto por precaucao
    dropTable();
    fts_table();
}

function copyerror(e)
{
    //esta versao do banco de dados ja existe.
    //abro o BD
    db = window.sqlitePlugin.openDatabase({name: dbName});
    //db3 = window.sqlitePlugin.openDatabase({name: "vtestudos"});
    //alert("copyerror" + JSON.stringify(e));
}


//---------------------------------------------------------------

function fts_table(){
    db.transaction(function(tx) {
    tx.executeSql('CREATE VIRTUAL TABLE vtestudos USING FTS3(titulo, texto, id_titulo)', [], function(tx,res){
          //alert("nao deu erro");
          //db = window.sqlitePlugin.openDatabase({name: "vtestudos"});
          //alert("uai. deu pra abrir");

          db.transaction(function(tx) {
          tx.executeSql('INSERT INTO vtestudos(titulo, texto, id_titulo) SELECT titulo, texto, id_titulo FROM estudos', [], function(tx,res){
              //db3 = window.sqlitePlugin.openDatabase({name: "vtestudos"});
               console.log('insert ok');
          });
          }, function(err){
              alert(err.message);
          });

    });
    }, function(err){
        alert(err.message);
    });
}

//---------------------------------------------------------------

function dropTable()
{
    window.plugins.sqlDB.remove("estudosprev1", 0, rmsuccess,rmerror); 
    window.plugins.sqlDB.remove("estudosprev2", 0, rmsuccess,rmerror);  
}

function rmsuccess()
{
    //existe versão anterior
    //alert("removesuccess");
    console.log('existe versão anterior');
}

function rmerror(e)
{
    //não existe versão anterior. ignoro.
    //alert("removeerror" + JSON.stringify(e));
    console.log('n existe versão anterior. ignoro.');
}

＆＃13;

未捕获的TypeError：无法读取未定义的属性'querySelector'

2 个答案: