效果：

　　Validate forms like you've never validated before!

自定义Validate：

doesn't jQuery make it easy to write your own validation plugin?
- Sure, but there are still a lot of subtleties to take care of:
  - You need a standard library of validation methods (such as emails, URLs, credit card numbers).
  - You need to place error messages in the DOM and show and hide them when appropriate.
  - You want to react to more than just a submit event, like keyup and blur.
  - You may need different ways to specify validation rules according to the server-side enviroment you are using on different projects.

集成好的、拿来即用的Validate

there are a lot of non-jQuery-based solutions (which you'd avoid since you found jQuery) and some jQuery-based solutions
This particular one is one of the oldest jQuery plugins (started in July 2006) and has proved itself in projects all around the world.
- There is also an article discussing how this plugin fits the bill of the should-be validation solution.
- ```
<form class="cmxform" id="commentForm" method="get" action="">
  <fieldset>
    <legend>Please provide your name, email address (won't be published) and a comment</legend>
    <p>
      <label for="cname">Name (required, at least 2 characters)</label>
      <input id="cname" name="name" minlength="2" type="text" required>
    </p>
    <p>
      <label for="cemail">E-Mail (required)</label>
      <input id="cemail" type="email" name="email" required>
    </p>
    <p>
      <label for="curl">URL (optional)</label>
      <input id="curl" type="url" name="url">
    </p>
    <p>
      <label for="ccomment">Your comment (required)</label>
      <textarea id="ccomment" name="comment" required></textarea>
    </p>
    <p>
      <input class="submit" type="submit" value="Submit">
    </p>
  </fieldset>
</form>
<script>
$("#commentForm").validate();
</script>
```
  - A single line of jQuery to select the form and apply the validation plugin, plus a few annotations on each element to specify the validation rules.
    - Of course that isn't the only way to specify rules. You also don't have to rely on those default messages, but they come in handy when starting to setup validation for a form.
- 效果
  - After trying to submit an invalid form, the first invalid element is focused, allowing the user to correct the field.
    - If another invalid field – that wasn't the first one – was focused before submit, that field is focused instead, allowing the user to start at the bottom if he or she prefers.
  - Before a field is marked as invalid, the validation is lazy:
    - Before submitting the form for the first time, the user can tab through fields without getting annoying messages – they won't get bugged before having the chance to actually enter a correct value
  - Once a field is marked invalid, it is eagerly validated:
    - As soon as the user has entered the necessary value, the error message is removed
  - If the user enters something in a non-marked field, and tabs/clicks away from it (blur the field), it is validated
    - obviously the user had the intention to enter something, but failed to enter the correct value
- 原理
  - That behaviour can be irritating when clicking through demos of the validation plugin
    - it is designed for an unobtrusive user experience, annoying the user as little as possible with unnecessary error messages.

API

two terms are used very often, so it's important that you know their meaning in the context of the validation plugin:

method:A validation method implements the logic to validate an element,
like an email method that checks for the right format of a text input's value.

A set of standard methods is available, and it is easy to write your own.
List of built-in Validation methods:A set of standard validation methods is provided:

equalTo – Requires the element to be the same as another on

Some more methods are provided as add-ons, and are currently included in additional-methods.js in the download package. Not all of them are documented here:
- accept – Makes a file upload accept only specified mime-types.
- creditcard – Makes the element require a credit card number.
- extension – Makes the element require a certain file extension.
- phoneUS – Validate for valid US phone number.
- require_from_group – Ensures a given number of fields in a group are complete.
- You can find the source code for all additional methods in the GitHub repository.
- It is possible to re-define the implementation of the built-in rules using the $.validator.methods property
A validation method implements the logic to validate any element.
- Provided are a set of default validation methods, such as required.
- Apart from required itself and equalTo, all validation methods declare an element valid when it has no value at all. That way an email field is optional unless required is specified.
- You can specify an element input to contain a valid email address, or nothing at all. Use jQuery.validator.addMethod to implement custom methods.

rule: A validation rule associates an element with a validation method
- like "validate input with name "primary-mail" with methods "required" and "email".
- A validation rule applies one or more validation methods to an input element.
- You can specify validation rules via metadata or via plugin settings (option rules).
  - The decision is often influenced by serverside infrastructure.
    - If a web framework is used, it is often easier to use metadata, which is also good for fast prototyping.
  - Plugin settings produce cleaner markup, though valid markup results from both.
- Whenever you have multiple fields with the same rules and messages, refactoring those can reduce a lot of duplication. Using addMethod and addClassRules are most effective for that.
  - Let's consider an example where you have ten customer fields, each required and with a minlength of 2. You need custom messages for both rules. To avoid having to specify those rules and messages again and again, we can alias existing methods with different messages and group them into a single class:
    - // alias required to cRequired with new message $.validator.addMethod("cRequired", $.validator.methods.required, "Customer name required"); // alias minlength, too $.validator.addMethod("cMinlength", $.validator.methods.minlength, // leverage parameter replacement for minlength, {0} gets replaced with 2 $.validator.format("Customer name must have at least {0} characters")); // combine them both, including the parameter for minlength $.validator.addClassRules("customer", { cRequired: true, cMinlength: 2 });　
    - With that in place, we can add a class customer to all customer fields and be done with it:
    - <input name="customer1" class="customer"> <input name="customer2" class="customer"> <input name="customer3" class="customer">
- You can also reuse existing methods inside other custom methods, to reuse certain implementations.
  - For example, if you're writing a custom method for validating email addresses inside a single field, you could call the existing email method for each email:
  - ```
  jQuery.validator.methods.email.call(this, email, element)
```

Plugin methods

This library adds three jQuery plugin methods, the main entry point being the validate method:

Custom selectors

This library also extends jQuery with three custom selectors:

Validation event

The goal of these interactions is to provide feedback as early as possible, whilst avoiding user annoyance.

Displaying error messages before the user had the chance to even type something is not helpful.

By default, forms are validated on submit, triggered by the user clicking the submit button or pressing enter when a form input is focused (option onsubmit).
In addition, once a field was highlighted as being invalid, it is validated whenever the user types something in the field (option onkeyup).
When the user enters something invalid into a valid field, it is also validated when the field loses focus (option onfocusout).

validator

The validate method returns a Validator object that has a few public methods that you can use to trigger validation programmatically or change the contents of the form

The validator object has more methods, but only those documented here are intended for usage.

There are a few static methods on the validator object:

Error messages

An error message displays a hint for the user about invalid elements, and what is wrong.

There are four ways to provide error messages.

Via the title attribute of the input element to validate
via data attributes,
via error labels
via plugin settings (option messages).

All validation rules included here provide a default error message which you can use for prototyping,because it is used when no specific message is provided.

The priorities are as follows:

A custom message (passed by plugin options),
the element's title,
the default message.

When using data attributes, you can set a generic message for all rules, or specific messages per rule:

<input required data-msg="Please fill this field">
<input data-rule-minlength="2" data-rule-maxlength="4" data-msg-minlength="At least two chars" data-msg-maxlength="At most fours chars">

Error message display

Error messages are handled via label elements with an additional class (option errorClass).

The link between the message and the invalid element is provided via the labels for attribute.

When provided in the markup, they are shown and hidden accordingly, and otherwise created on demand.

By default, labels are created after the invalid element, this is also customizable (option errorPlacement).

It is also possible to put them into an error container (option errorLabelContainer).

To use a different element then a label, specify the errorElement option.

General messages

In addition to field-specific messages you can display a general "your form is invalid, please fix the highlighted fields!" message in a container anywhere on your page,

eg. above the form (option errorContainer).

The container is shown and hidden when errors occur and are fixed accordingly.

The container for error labels (option errorLabelContainer) can also be nested inside the error container.

Focusing of invalid elements

By default, the first invalid element in a form is focused after submitting a form with invalid elements.

To prevent confusion on the behalf of the user, the plugin remembers the element that had focus when the form was submitted, and refocuses that element.

That way the user can try to fill out elements of the form at the end, without being forced to focus them again and again. This can be disabled (option focusInvalid).

General Guidelines

provides detailed discussion of the design and ideas behind the plugin,

explaining why certain things are as they are.

It covers the features in more detail than the API documentation, which just briefly explains the various methods and options available.

Fields with complex names (brackets, dots)

When you have a name attribute like user[name], make sure to put the name in quotes.

More details in the General Guidelines.

If your form consists of fields using names that aren't legal JavaScript identifiers, you have to quote those names when using the rules option:

 $("#myform").validate({
   rules: {
     // no quoting necessary
     name: "required",
     // quoting necessary!
     "user[email]": "email",
     // dots need quoting, too!
     "user.address.street": "required"
   }
 });

Too much recursion

Another common problem occurs with this code:

$("#myform").validate({
  submitHandler: function(form) {
    // some other code
    // maybe disabling submit button
    // then:
    $(form).submit();
  }
 });

This results in a too-much-recursion error:

$(form).submit() triggers another round of validation, resulting in another call to submitHandler, and voila, recursion.

Replace that with form.submit(), which triggers the native submit event instead and not the validation.

So the correct code looks slightly different:

 $("#myform").validate({
  submitHandler: function(form) {
    form.submit();
  }
 });

Form submit

By default, the form submission is prevented when the form is invalid, and submitted as normal when it is valid. You can also handle the submission manually (option submitHandler).

Skipping validation on submit

To skip validation while still using a submit-button, add the attribte "formnovalidate" to that input:

 <input type="submit" name="go" value="Submit">
 <input type="submit" formnovalidate name="cancel" value="Cancel">

This used to work by adding class="cancel" to the input, this is now deprecated.　　

Demo for the cancel button

Developing and debugging a form

While developing and debugging the form, you should set the debug option to true.

That prevents form submission on both valid and invalid forms and outputs some helpful messages to window.console (available via Firebug or Firebug Lite) that help debugging

When you have everything set up and don't get any error messages displayed, check if your rules all accept empty elements as valid (like email or url methods).

Some issues are caused by certain form element's names.

A name you should avoid is "submit" (for submit buttons and anything else).
- browsers expose form elements as properties of the form element, by their name, in this case hiding native methods like submit().　
- Just don't use name="submit" and you're good.

Validating multiple forms on one page

The plugin can handle only one form per call.

In case you have multiple forms on a single page which you want to validate, you have to initialise them all individually:

$( "form" ).each( function() {
  $( this ).validate( options );
} );

You can avoid having to duplicate the plugin settings by modifying the defaults, using jQuery.validator.setDefaults to override multiple settings at once.　

目标：

The ultimate goal of this plugin is to make working with forms more fun for everyone.

By improving the interaction, it is easier and less annoying for the user to fill out the form and submit it.

To achieve this, it is important that the plugin is actually deployed on websites around the world,

so a lot of focus is spent on making it easy for developers – that's you – to use the plugin.

The plugin can never replace serverside validation and doesn't intend to do so.

Having both in place gives you the necessary security for your application, as well as improved usability.

使用建议

Mandated: A 'name' attribute is required for all input elements needing validation, and the plugin will not work without this.
- A 'name' attribute must also be unique to the form, as this is how the plugin keeps track of all input elements.
- However, each group of radio or checkbox elements will share the same 'name' since the value of this grouping represents a single piece of the form data.
Optionally: Each input can have a label associated with it, where the 'for' attribute of the label refers to the 'id' attribute of the input.
- It's also a common practice to have 'id' and 'name' attributes with the same value, although keep in mind that since this plugin does not use the 'id' attribute, this is not mandatory.

<label for="firstname">Firstname</label>
<input id="firstname" name="fname">

秒客网

jQuery validator plugin之概要