如何在 JavaScript 中实现“添加新项目”功能？

Question

The title isn't very descriptive but I couldn't find a better one. Feel free to edit it.

Basically what I'm looking for is the best way to do the following:

When the user clicks "Add New Item", a new row is added with an indentical text box and drop down as above. The options I can think of are the following:

• Hardcode the HTML in the JavaScript code. This is obviously a hideously ugly solution.
• Assemble the HTML from DOM nodes (or jQuery objects). This is very ugly too.
• Use a client-side template system. I used one of those once and it was pretty weird (it used <script language="html"> tags to define the templates).
• Make an ad-hoc client-side "template" and hide it somehow with CSS.
• Make an AJAX request to fetch the HTML. This is slow and uses server resources unnecessarily.

What do you suggest? I'm not completely satisfied with any of the above solutions.

Answer 1

If you're already using a framework like jquery or sencha on your page, you might as well make use of it.

Otherwise, i'd keep it as simple as possible. This does't look like a very important core functionality, so don't create something that requires extra https requests or even entire libraries to be loaded. Cloning or generating the html might not look elegant, but it'll be:

• fast to implement
• easy to read, and therefore easy to debug
• waste few resources, and extremely fast
• stable
• doesn't need server side code or extra http requests
• it'll be easy to change the implementation later on if needed

Don't create something that's overkill for somerhing as trivial as this.

Answer 2

Assuming the super-simple approach and that your format is in a table:

<table>
    <tr>
        <td><input type="text" name="item_name" placeholder="item name" /></td>
        <td><select name="item_type"><option value="" selected="selected">Type</option></select></td>
    </tr>
    <tr>
        <td><input type="text" name="item_name" placeholder="item name" /></td>
        <td><select name="item_type"><option value="" selected="selected">Type</option></select></td>
    </tr>
    <tr>
        <td colspan="2" id="add">+ Add new item</td>
    </tr>
</table>

You can use the following:

$('#add').on('click',function(e){
    var $this = $(this);
    var $newRow = $this.closest('table').find('tr:first').clone();
    $newRow.find(':input').val('');
    $newRow.insertBefore($this.parent());
});

Broken down:

1. We give the last item an ID to make it easier to bind a click event to.
2. Use jQuery and bind the click event to that ID which:
   • Grabs the current table we're clicking within ( $this.closest('table') )
   • Locates the first row within that table and duplicates it ( .clone() )
   • Remove any populated values that may be present ( .find(':input').val('') )
   • Append this new cloned row to the table just above the "add new item" row ( $newRow.insertBefore(...) )

You can also take the template approach, but that's really up to you and how much control you'd like over the output.

Answer 3

While I realise you already have an accepted answer, I thought I'd offer a plain JavaScript means of achieving the same:

function closest(el, tag) {
    if (!el || !tag) {
        return false;
    }
    else {
        var curTag = el.tagName.toLowerCase();
        return curTag == tag.toLowerCase() && curTag !== 'body' ? el : closest(el.parentNode, tag);
    }
}

function addRow(el) {
    if (!el) {
        return false;
    }
    else {
        var tr = closest(el, 'tr').previousElementSibling,
            newRow = tr.cloneNode(true);
        tr.parentNode.insertBefore(newRow, tr.nextSibling);
    }
}

document.getElementById('add').onclick = function() {
    addRow(this);
}​

JS Fiddle demo .

Revised the above a little, to add a simple shim to cope with those browsers that don't implement previousElementSibling :

function closest(el, tag) {
    if (!el || !tag) {
        return false;
    }
    else {
        var curTag = el.tagName.toLowerCase();
        return curTag == tag.toLowerCase() && curTag !== 'body' ? el : closest(el.parentNode, tag);
    }
}

function prevElementSiblingShim(el) {
    if (!el) {
        return false;
    }
    else {
        var prevSibling = el.previousSibling;
        return prevSibling.nodeType == 1 ? prevSibling : prevElementSiblingShim(prevSibling);
    }
}

function addRow(el) {
    if (!el) {
        return false;
    }
    else {
        var par = closest(el, 'tr'),
            tr = par.previousElementSibling || prevElementSiblingShim(par),
            newRow = tr.cloneNode(true);
        tr.parentNode.insertBefore(newRow, tr.nextSibling);
    }
}

document.getElementById('add').onclick = function() {
    addRow(this);
}​

References:

• cloneNode() .
• insertBefore .
• nextSibling .
• nodeType .
• parentNode .
• previousElementSibling ^{Compatibility} .
• previousSibling .
• tagName .
• toLowerCase() .

Answer 4

Inserting HTML from a string into the DOM is the most efficient way. Unless you're inserting hundreds at once, it doesn't really matter.