.prop() vs .attr()

 

So jQuery 1.6 has the new function prop() . 

$(selector).click(function(){
    //instead of:
    this.getAttribute('style');
    //do i use:
    $(this).prop('style');
    //or:
    $(this).attr('style');
})

or in this case do they do the same thing?

And if I do have to switch to using prop() , all the old attr() calls will break if i switch to 1.6?

UPDATE 

selector = '#id'

$(selector).click(function() {
    //instead of:
    var getAtt = this.getAttribute('style');
    //do i use:
    var thisProp = $(this).prop('style');
    //or:
    var thisAttr = $(this).attr('style');

    console.log(getAtt, thisProp, thisAttr);
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.6.0/jquery.min.js"></script>
<div id='id' style="color: red;background: orange;">test</div>

Update 1 November 2012

My original answer applies specifically to jQuery 1.6. My advice remains the same but jQuery 1.6.1 changed things slightly: in the face of the predicted pile of broken websites, the jQuery team reverted attr() to something close to (but not exactly the same as) its old behaviour for Boolean attributes. John Resig also blogged about it. I can see the difficulty they were in but still disagree with the recommendation to prefer attr() .

Original answer

If you've only ever used jQuery and not the DOM directly, this could be a confusing change, although it is definitely an improvement conceptually. Not so good for the bazillions of sites using jQuery that will break as a result of this change though.

I'll summarize the main issues:

  • You usually want prop() rather than attr() .
  • In the majority of cases, prop() does what attr() used to do. Replacing calls to attr() with prop() in your code will generally work.
  • Properties are generally simpler to deal with than attributes. An attribute value may only be a string whereas a property can be of any type. For example, the checked property is a Boolean, the style property is an object with individual properties for each style, the size property is a number.
  • Where both a property and an attribute with the same name exists, usually updating one will update the other, but this is not the case for certain attributes of inputs, such as value and checked : for these attributes, the property always represents the current state while the attribute (except in old versions of IE) corresponds to the default value/checkedness of the input (reflected in the defaultValue / defaultChecked property).
  • This change removes some of the layer of magic jQuery stuck in front of attributes and properties, meaning jQuery developers will have to learn a bit about the difference between properties and attributes. This is a good thing.

    • If you're a jQuery developer and are confused by this whole business about properties and attributes, you need to take a step back and learn a little about it, since jQuery is no longer trying so hard to shield you from this stuff. For the authoritative but somewhat dry word on the subject, there's the specs: DOM4, HTML DOM, DOM Level 2, DOM Level 3. Mozilla's DOM documentation is valid for most modern browsers and is easier to read than the specs, so you may find their DOM reference helpful. There's a section on element properties.

    As an example of how properties are simpler to deal with than attributes, consider a checkbox that is initially checked. Here are two possible pieces of valid HTML to do this: 

    <input id="cb" type="checkbox" checked>
<input id="cb" type="checkbox" checked="checked">

    So, how do you find out if the checkbox is checked with jQuery? Look on Stack Overflow and you'll commonly find the following suggestions:

  • if ( $("#cb").attr("checked") === true ) {...}
  • if ( $("#cb").attr("checked") == "checked" ) {...}
  • if ( $("#cb").is(":checked") ) {...}

    • This is actually the simplest thing in the world to do with the checked Boolean property, which has existed and worked flawlessly in every major scriptable browser since 1995:

    if (document.getElementById("cb").checked) {...}

    The property also makes checking or unchecking the checkbox trivial:

    document.getElementById("cb").checked = false

    In jQuery 1.6, this unambiguously becomes

    $("#cb").prop("checked", false)

    The idea of using the checked attribute for scripting a checkbox is unhelpful and unnecessary. The property is what you need.

  • It's not obvious what the correct way to check or uncheck the checkbox is using the checked attribute
  • The attribute value reflects the default rather than the current visible state (except in some older versions of IE, thus making things still harder). The attribute tells you nothing about the whether the checkbox on the page is checked. See http://jsfiddle.net/VktA6/49/.

    • This change has been a long time coming for jQuery. For years, they've been content with a function named attr() that mostly retrieved DOM properties, not the result you'd expect from the name. The segregation of attr() and prop() should help alleviate some of the confusion between HTML attributes and DOM properties. $.fn.prop() grabs the specified DOM property, while $.fn.attr() grabs the specified HTML attribute.

    To fully understand how they work, here's an extended explanation on the difference between HTML attributes and DOM properties.:

    HTML Attributes

    Syntax:

    <body onload="foo()">

    Purpose: Allows markup to have data associated with it for events, rendering, and other purposes.

    Visualization: HTML属性 The class attribute is shown here on the body. It's accessible through the following code: 

    var attr;
attr = document.body.getAttribute("class");
//IE 8 Quirks and below
attr = document.body.getAttribute("className");

    Attributes are returned in string form and can be inconsistent from browser to browser. However, they can be vital in some situations. As exemplified above, IE 8 Quirks Mode (and below) expects the name of a DOM property in get/set/removeAttribute instead of the attribute name. This is one of many reasons why it's important to know the difference.

    DOM Properties

    Syntax:

    document.body.onload = foo;

    Purpose: Gives access to properties that belong to element nodes. These properties are similar to attributes, but are only accessible through JavaScript. This is an important difference that helps clarify the role of DOM properties. Please note that attributes are completely different from properties , as this event handler assignment is useless and won't receive the event (body doesn't have an onload event, only an onload attribute).

    Visualization: DOM属性

    Here, you'll notice a list of properties under the "DOM" tab in Firebug. These are DOM properties. You'll immediately notice quite a few of them, as you'll have used them before without knowing it. Their values are what you'll be receiving through JavaScript.

    Documentation

  • JavaScript: The Definitive Guide by David Flanagan
  • HTML Attributes, Mozilla Dev Center
  • DOM Element Properties, Mozilla Dev Center

    • Example

    HTML: <textarea id="test" value="foo"></textarea>

    JavaScript: alert($('#test').attr('value'));

    In earlier versions of jQuery, this returns an empty string. In 1.6, it returns the proper value, foo .

    Without having glanced at the new code for either function, I can say with confidence that the confusion has more to do with the difference between HTML attributes and DOM properties, than with the code itself. Hopefully, this cleared some things up for you.

    -Matt

    链接地址: http://www.djcxy.com/p/27552.html

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