javascript：未定义的变量

Question

my variable 'todoList' is showing up as undefined. i am very new to javascript and programming in general. any help would greatly be appreciated!

 var todoList = { todos:[], displayTodos: function() { if (this.todos.length === 0) { console.log ('Your todos list is empty!'); } else { console.log('My Todos:'); for (var i = 0; i < this.todos.length; i++) { if (this.todos[i].completed === true) { console.log ('(x)', this.todos[i].todoText); } else { console.log('( )', this.todos[i].todoText); } } } }, addTodo: function(todoText) { this.todos.push({ todoText: todoText, completed: false }); this.displayTodos(); }, changeTodo: function(position, todoText) { this.todos[position].todoText = todoText; this.displayTodos(); }, deleteTodo: function(position) { this.todos.splice(position, 1); this.displayTodos(); }, toggleCompleted: function(position) { var todo = this.todos[position]; todo.completed = !todo.completed; this.displayTodos(); }, toggleAll: function() { var totalTodos = this.todos.length; var completedTodos = 0; for (var i = 0; i < totalTodos; i++) { if(this.todos[i].completed === true) { completedTodos++; } } if (completedTodos === totalTodos) { for(var i =0; i < totalTodos; i++) { this.todos[i].completed === false; } } this.displayTodos; } }; 

Answer 1

JavaScript always returns something . If I copy/paste your code into the Chrome console and run it, it tells me the returned result of running that code is undefined . That's okay, since you're just setting up the object and have no intention of using the return value.

After this, the object has been created and typing it into the Chrome console tells us that the variable todoList is an object.