Learn TypeScript 3 by Building Web Applications

Creating the TodoList class

Now, you can also implement the TodoList class:

class TodoList { 
    private _todoList: ReadonlyArray<TodoItem> = []; 

    constructor(todoList?: TodoItem[]) { 
        // first we make sure that we have received a valid array 
        // reference: https://developer.mozilla.org/en-        // US/docs/Web/JavaScript/Reference/Global_Objects        // /Array/isArray 
        if(Array.isArray(todoList) && todoList.length) { 
            this._todoList = this._todoList.concat(todoList); 
        } 
    } 

    get todoList(): ReadonlyArray<TodoItem> { 
        return this._todoList 
    } 

    addTodo(todoItem: TodoItem) { 
        if(todoItem) { 
            // the value is "truthy": 
            // not null, not undefined, not NaN, not an empty string,  // not 0, not false this._todoList = this._todoList.concat(todoItem); } } removeTodo(itemId: string) ...