Why jQuery 1.9+ attr() method not deprecated?

Question

Can I, a jQuery1.9+ software developer, "deprecate" the use of the attr() method in my day-by-day work?

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As showed in many questions,

• .prop() vs .attr() (main)
• jQuery attr vs. prop, there are a list of props?
• jQuery attr vs prop?
• Migrating jQuery 1.8.3 to 1.9.0 - Replacing deprecated .attr()
• ... etc. ...

there are a lot of confusion about "use attr or use prop?", and, by my (developer's) view point, for all uses of attr() method, we can use prop instead:

1. backward-compatibility: coding new software not need this;
2. performance: John says "Accessing properties through the .attr() method will be slightly slower than accessing them directly through .prop()";
3. Change attribute value: all can be changed by the prop(name,newvalue) method.
4. Remove attribute: all can be removed by the removeProp(name) method.
5. Check HTML attribute values: browser use DOM, all HTML was converted to DOM, and, if DOM affected the attr(name) method also affected. About "strong type" of prop: it is better than "html string value" (ex. "checked" vs true).
6. Check if an attribute was defined in the "HTML original code" (supposing that method attr in your browser returns undefined if it is not)... Well, we need this in some piece of software? At forms, ".val() method is the recommended jQuery way to get or set the values of form"
7. Cross-browser consistency: both (not only attr) are consistent methods. (it is??).

So, at this time (2013), I not see a good reason to use attr method when developing new jQuery code... But, well, this is, in other words, the question: There are a good reason to use attr method in my day-by-day tasks?

Answer 1

.attr() is not deprecated because it's useful for what it's made for, and is the only correct way to do what it's made for (short of using each element's getAttribute function, which does the same thing...or parsing the HTML yourself). The only reason we are even having this discussion at all is because jQuery (and some old browsers (cough IE cough)) incorrectly conflated attributes and properties, and that muddling is what they apparently fixed in 1.9.

.attr() retrieves attributes, while .prop() retrieves properties. The two are different things, and always officially have been (though the DOM often has a property to correspond to an attribute). If you have a <p whatever="value">, where whatever is not an attribute the browser recognizes, you'd use .attr() to get the attribute's value. .prop() wouldn't even be able to see it in most browsers.

When you care about the resulting DOM property, use .prop(). When you care about the actual HTML attribute, use .attr(). It's not really an either/or thing; you can use both in the same code and the universe won't implode even once (assuming you've used them correctly, anyway). :) Just use the one that's suited to the job you're doing at the time, and quit trying to "deprecate" stuff that's not broken.

Answer 2

I took the liberty of preparing a fiddle for you:

http://jsfiddle.net/5REVP/

Especially this part:

<div id="example" style="padding:10px"></div>

console.log("style");
var styleAttr = $("#example").attr("style");
console.log(styleAttr); // You get "padding:10px"
var styleProp = $("#example").prop("style");
console.log(styleProp); // You get a CSSStyleDeclaration object

The "style" example shows clearly that an attribute is not the same as a property (check the console).

For readability, maintainability and backward (as well as forward) compatibility you should allways use the correct methods for a given task, otherwise there is a chance that a method may stop behaving as you though it would, the .attr() method is an example of that.

.attr() method is used to get attributes of elements, attributes are a SGML term that refers to the information contained inside the element tags, you can easily read that information by inspecting the elements.

• If you get the "style" attribute of an element you will not get any information other than what is specifically written in that attribute.
• If you get the "checked" attribute of a checkbox you will either get "checked" or "".

.prop() method is used to get DOM properties of elements.

• If you get the "style" property you are not getting what the designer wrote in the style attribute, you are getting all the actual css properties of the element.
• If you get the "checked" property of a checkbox you will get true or false.

Answer 3

.attr() only accesses HTML attributes, whereas .prop() will retrieve properties not on the HTML elements. See the documentation:

For example, selectedIndex, tagName, nodeName, nodeType, ownerDocument, defaultChecked, and defaultSelected should be retrieved and set with the .prop() method. Prior to jQuery 1.6, these properties were retrievable with the .attr() method, but this was not within the scope of attr. These do not have corresponding attributes and are only properties.

http://api.jquery.com/prop/

Answer 4

My homework... After read @cHao and @cernunnos good explanations, and after some months using it... I thing we need another concept to decide, as programmer, when use or not prop and attr:

• HTML source-code and its representation: the browser loads HTML page in the browser's memory space. Well, what stay at memory's browser is the DOM representation, but DOM preserves some original things, as attributes and cssText property, that are "sometimes persisted representations".
  PS: attributes that are not defined in the "standard DOM", have not a mapping to DOM properties. When one (not read-only) attribute changes, if there are corresponding (mapped) property, it can be changed automaticlally.

• DOM state: dynamical pages need changes directly at the DOM, that is what final users see. So, if there are some "click and change" actions at the page, each time the DOM goes to a new page representation, so, each time DOM have a new state.
  When one DOM-property changes, all other DOM properties (if need) changes consistently.

With these concepts in mind, we can draw a "rule of thumb (for attr vs prop uses)":

1. Use prop, you have 90% of chances that it works... 99% if you using jQuery for change DOM states (and standard DOM hypothesis).
2. If you need to change or access to data-* attributes, use .data() method.
3. Otherwise (non-DOM, non-data, or non-standard things) check if a case of use .attr(), and reserve some time to study it (see answers above).