为什么不能读入输入值并显示警报？

Question

I've looked this up and tried it out but it isn't working. If the user submits a in the input field, then it should alert it works but for some reason it isn't working.

What am I doing wrong and how can I fix it?

 $(function() { var $list, $newItemForm; $list = $('ul'); $newItemForm = $("newItemForm"); $newItemForm.on('submit', function(e) { e.preventDefault(); // var text = $('input:text').val(); var text = $('itemField').val(); console.log(text); $list.append('<li>' + text + '</li>'); // $('input:text').val(''); if (text == "a") { alert("it works"); } }); }); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <form id="newItemForm"> <input type="text" id="itemField" placeholder="item" /> <input type="submit" id="add" value="add" /> </form> 

Answer 1

You forgot to prefix # in the selector while referencing the form ( $("newItemForm") ) and input value ( $('itemField').val() ) in variables:

 $(function() { var $list, $newItemForm; $list = $('ul'); $newItemForm = $("#newItemForm"); $newItemForm.on('submit', function (e) { e.preventDefault(); // var text = $('input:text').val(); var text = $('#itemField').val(); console.log(text); $list.append('<li>' + text + '</li>'); // $('input:text').val(''); if(text == "a") { alert("it works"); } }); }); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <form id="newItemForm"> <input type="text" id="itemField" placeholder="item"/> <input type="submit" id="add" value="add"/> </form> 

Answer 2

I think the problem is with the selectors for "newItemForm" and "itemField".

In jQuery, when you want to select elements by ID you need to prepend the # character.

The code should be as follows:

$(function() {
var $list, $newItemForm;
$list = $('ul');
$newItemForm = $("#newItemForm"); // Remember to use # to select by ID.

$newItemForm.on('submit', function (e) {
    e.preventDefault();
    // Get value from item field.
    var text = $('#itemField').val(); // Use # here as well.
    // Clear the item field.
    $('#itemField').val('');
    console.log(text);
    $list.append('<li>' + text + '</li>');

    if(text == "a") {
        alert("it works");
    }
});

});

If you don't use #, jQuery expects what follows to be an element type, for instance ul or span or the like. If you want to select by class you need to prepend a . in front of the class name, for instance ".classname".

I hope this helps.