1. <!DOCTYPE html>
    2. <html lang="en">
    3. <head>
    4.     <meta charset="UTF-8">
    5.     <meta name="viewport" content="width=device-width, initial-scale=1.0">
    6.     <title>Document</title>
    7. </head>
    8. <body>
    9.     <!-- todoList -->
    10.     <input type="text" id="input">
    11.     <ul id="app">
    13.     </ul>
    14.     <script>
    15.         var arr = [];
    16.         var input = document.getElementById("input");
    17.         var app = document.getElementById("app");
    18.         input.onkeydown = function (event) {
    19.             if (event.keyCode == 13) {
    20.                 if (arr.indexOf(this.value) == -1  && this.value!= "") {
    21.                     arr.push(this.value);
    22.                     var li = document.createElement("li");
    23.                     li.innerHTML = this.value;
    24.                     app.append(li);
    25.                 }
    26.             }
    28.         }
    29.     </script>
    30. </body>
    31. </html>

    1.PNG