javascript - Store jquery selector in variable

Question

Welcome To Ask or Share your Answers For Others

javascript - Store jquery selector in variable

posted Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

javascript - Store jquery selector in variable

In the following example the stored jQuery selector returns the wrong value. There is a possibility to store the selectors and not the result?

The js code:

// storing the jQuery selectors
var
  $container = $( '.container' ),
  $element1  = $container.find( '.element' ),
  $element2  = $( '.element', $container ),
  $element3  = $( '.element' );

// append elements to the container
for( i=0; i<10; ++i ){
  $container.append( $(element_html) );  
}

// try the stored selectors -> returns 0
console.log( "1: " + $element1.length );
console.log( "2: " + $element2.length );
console.log( "3: " + $element3.length );

Why, if I use the container selectors to find the elements, it works? It is beacuse the selector returns the pointer to the matched elements and not the elements?

// this works
console.log( "1: " + $container.find( '.element' ).length );
console.log( "2: " + $( '.element', $container )  .length );
console.log( "3: " + $( '.element' )              .length );

jsFiddle demonstration

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…

1 Reply

深蓝 · Answer 1 · 2021-10-16T23:52:16+0000

You have a fundamental misunderstanding of what

variableName = $("selector here");

does. It does not "store the selector." It runs the selector you give against the current elements in the DOM, creates a jQuery object, puts the matching elements in the jQuery object, and gives you a reference to that jQuery object. The selector is not stored (modulo jQuery internals).

So given:

<body>
<div class="foo">x</div>
</body>

Then:

var $divs = $("div.foo");
console.log($divs.length);        // 1

Gives us this:

$divs jQuery object pointing at one div in the DOM

If we then add another matching div:

$('<div class="foo"></div>').appendTo(document.body);

Our $divs still only points to the first one; adding another matching element to the DOM had no effect on the jQuery object referenced from $divs.

$divs jQuery object pointing to one div, but there are two in the DOM

If we re-run the query at that point:

$divs = $("div.foo");

...then we have:

$divs jQuery object pointing at both divs in the DOM

If you have a jQuery object containing a DOM element, and you add descendant elements to that DOM element, then using that jQuery object with (say) .find will see the descendants. That's because the parent DOM element is already there in the jQuery object. E.g., adding a span to one of the divs that we already reference from our jQuery object:

$divs jQuery object pointing at both divs in the DOM, one has a span now

If we were to use .find on $divs at that point looking for a span, we'd find it, because it's a descendant of one of the elements we already had a reference to.

If you want to re-run the DOM search again later to look for matching elements, you just use $() again; this is implicit in the above, but for clarity:

var $divs = $("div.foo");
console.log($divs.length);        // 1
$('<div class="foo"></div>').appendTo(document.body);
console.log($divs.length);        // Still 1
$divs = $("div.foo");
console.log($divs.length);        // Now it's 2

So "storing a selector," when needed, is a matter of storing the selector string somewhere, not the jQuery object.

Categories

javascript - Store jquery selector in variable

javascript - Store jquery selector in variable

Please log in or register to add a comment.

Please log in or register to reply this article.

1 Reply

Please log in or register to add a comment.

Just Browsing Browsing

Most popular tags