jquery filtering has + not

问题:

Okay I have list items, some have a span, some not.
On my event I want to add the span when they don't have any yet.

has() works fine, but not() adds the span to both??

HTML:

<ul>
    <li>
        <p>item</p>
        <span class="spn">empty span</span>
    </li>
    <li>
        <p>item 2</p>
    </li>
<ul>
<hr>
<a class="add-span"href="#">check</a>

JS:

$("a.add-span").click(function() {
    $("li").each(function(index) {
        // $(this).has("span").find("span").append(" - appended");
        $(this).not("span").append('<span class="spn">new span<\/span>');
    })    
})

回答1:

You can use a combination of the :not and :has selectors like this

$("a.add-span").click(function() {
    $("li:not(:has(span))").each(function(index) {
        $(this).append('<span class="spn">new span<\/span>');
    });
});

Here is a demo http://www.jsfiddle.net/xU6fV/

回答2:

$("a.add-span").click(function() {
    $("li").each(function(index) {
       if ($(this).children('span').length === 0){
         $(this).append('<span class="spn">new span<\/span>');
       }
    })    
})

With children() method, the length property is used to check whether or not a span already exits and if it doesn't, one is added/appended.

More Info:

• http://api.jquery.com/length/
• http://api.jquery.com/children/

回答3:

The accepted answer works well, if you don't want to filter out only those elements which do have the spans as direct children.

As the :has() and the .has() loop over all descendants, not just the children.

In that case, you have to use a function

$("li").not(function() {
    // returns true for those elements with at least one span as child element
    return $(this).children('span').length > 0 
}).each(function() { /* ... */ })

回答4:

Try this,

$("a.add-span").click(function() {
    $("li:not(:has(span))").each(function(index) {
        $(this).append($("<span class='spn'>").html("Newly Added Span"));
    });
});

回答5:

This is the first link on Google when searching "jquery not has". The specific scenario I needed to solve was a little different to this one. I had to not items that have a specific DOM element, not simply based on a tag. This meant I couldn't use a selector which each solution above used.

jQuery's has() however does accept a DOM element! So I created a jQuery plugin to combine these two inbuilt functions.

I wanted to share it here because hopefully it will help others in my situation too. It also answers the original question.

The Plugin:

(function ( $ ) {
    $.fn.extend({
        not_has: function (param) {
            return this.not(this.has(param));
        }
    });
}( jQuery ));

Implementation:

$("a.add-span").click(function() {
    $("li").not_has("span")
    .append('<span class="spn">new span<\/span>');

    // Prevent the page from navigating away
    return false;
});

https://jsfiddle.net/brjkg10n/1/

---

I was initially intending to find a jQuery function that would work like addBack() but using not instead. If you need something so complicated, then please feel free to use the following plugin.

(function ( $ ) {
    $.fn.extend({
        notBack: function () {
            return this.prevObject.not(this);
        }
    });
}( jQuery ));

With this, the answer would be:

$("li").has("span").notBack()
.append('<span class="spn">new span<\/span>');

https://jsfiddle.net/2g08gjj8/1/