Peter Lubbers - Pro HTML 5 Programming

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Download from Wow! eBook 182 CHAPTER 7 ■ USING THE <strong>HTML</strong>5 FORMS API Details: The pattern attribute gives developers a powerful and flexible way of enforcing a regular expression pattern on the value of a form control. When a pattern is set on a control, the patternMismatch will return true whenever the value does not conform to the rules of the pattern. To assist users and assistive technology, you should set the title on any pattern-controlled field to describe the rules of the format. tooLong Purpose: Make sure that a value does not contain too many characters Usage: Put a maxLength attribute on the form control Usage example: Details: This humorously-named constraint will return true if the value length exceeds the maxLength. While form controls will generally try to enforce the maximum length during user entry, certain situations including programmatic settings can cause the value to exceed the maximum. rangeUnderflow Purpose: Enforce the minimum value of a numeric control Usage: Set a min attribute with the minimum allowed value Usage example: Details: In any form controls that do numeric-range checking, it is possible for the value to get temporarily set below the allowable range. In these cases, the ValidityState will return true for the rangeUnderflow field. rangeOverflow Purpose: Enforce the maximum value of a numeric control Usage: Set a max attribute with the maximum allowed value Usage example: Details: Similar to its counterpart rangeUnderflow, this validity constraint will return true if the value of a form control becomes greater than the max attribute. stepMismatch Purpose: Guarantee that a value conforms to the combination of min, max, and step Usage: Set a step attribute to specify the granular steps of a numeric value Usage example: Details: This constraint enforces the sanity of the combinations of min, max, and step. Specifically, the current value must be a multiple of the step added to the minimum value. For example, a range from 0 to 100 with steps at every 5 would not allow a value of 17 without stepMismatch returning true.
CHAPTER 7 ■ USING THE <strong>HTML</strong>5 FORMS API customError Purpose: Handle errors explicitly calculated and set by the application code Usage: Call setCustomValidity(message) to put a form control into the customError state Usage example: passwordConfirmationField.setCustomValidity("Password values do not match."); Details: For those cases where the built-in validity checks don’t apply, the custom validity errors can suffice. Application code should set a custom validity message whenever a field does not conform to semantic rules. One common use case for custom validity is when consistency between controls is not achieved, for example if password confirmation fields don’t match. (We’ll delve into this specific example in the “Practical Extras” section.) Whenever a custom validity message is set, the control will be invalid and return the customError constraint as true. To clear the error, simply call setCustomValidity("") on the control with an empty string value. Validation Fields and Functions Together, these eight constraints allow a developer to find out exactly why a given form control is failing a validation check. Or, if you don’t care which specific reason is causing the failure, simply access the Boolean value valid on the ValidityState; it is an aggregate of the other eight constraints. If all eight constraints return false, then the valid field will return true. There are a few other helpful fields and functions on the form controls which can assist you in programming for validation checking. The willValidate Attribute The willValidate attribute simply indicates whether validation will be checked on this form control at all. If any of the above constraints—e.g. the required attribute, pattern attribute, etc.—are set on the control, the willValidate field will let you know that validation checking is going to be enforced. The checkValidity Function The checkValidity function allows you to check validation on the form without any explicit user input. Normally, a form’s validation is checked whenever the user or script code submits the form. This function allows validation to be done at any time. ■ Note Calling checkValidity on a form control doesn’t just check validation, it causes all resulting events and UI triggers to occur just as if the form had been submitted. The validationMessage Attribute This attribute isn’t yet supported by any current browser versions, but it might be by the time you read this. The validationMessage attribute lets you query programmatically a localized error message that the browser would display based on the current state of validation. For example, if a required field has no 183
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THE EXPERT’S VOICE ® IN WEB DEVE
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■ ■ ■ Pro HTML5 Programming P
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For my beautiful wife, Vittoria, an
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Contents ■Foreword ..............
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■ CONTENTS Implementing Canvas Se
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■ CONTENTS Summary ..............
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■ CONTENTS Setting and Retrieving
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Foreword In June 2004, representati
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About the Technical Reviewer � Pa
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Introduction HTML5 is brand new. In
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C H A P T E R 1 ■ ■ ■ Overvie
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CHAPTER 1 ■ OVERVIEW OF HTML5 wit
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Interoperability Simplification CHA
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• MathML • Microdata • Server
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Figure 1-1. A page rendered in stan
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Table 1-2. New sectioning HTML5 ele
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CHAPTER 1 ■ OVERVIEW OF HTML5 Wit
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article { background-color: #eee; d
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Figure 1-2. An HTML5 page with all
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CHAPTER 1 ■ OVERVIEW OF HTML5 All
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26 CHAPTER 2 ■ USING THE HTML5 CA
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C H A P T E R 3 ■ ■ ■ Working
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Audio and Video Codecs CHAPTER 3
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MEDIA FOR EVERYONE CHAPTER 3 ■ WO
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CHAPTER 3 ■ WORKING WITH HTML5 AU
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find the actual frame since the vid
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LOSING VIEWERS IN THE OF AN EYE CH
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C H A P T E R 4 ■ ■ ■ Using t
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A device can use any of the followi
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Table 4-4. Pros and cons of cell ph
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Figure 4-1. HTML5 Geolocation brows
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Listing 4-6. The Haversine formula
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THE EASIEST WAY TO TRAVEL CHAPTER 4
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var deltaLatitude = toRadians(latit
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Practical Extras CHAPTER 4 ■ USIN
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Show Me on a Google Map CHAPTER 4
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C H A P T E R 5 ■ ■ ■ Using t
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CHAPTER 5 ■ USING THE COMMUNICATI
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var defaultTitle = "Portal [http://
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Send Notification CHAPTER 5 ■ U
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Figure 5-4. Difference between clie
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“SEEMINGLY ARBITRARY” TIMES CHA
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C H A P T E R 11 ■ ■ ■ The Fu
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CHAPTER 11 ■ THE FUTURE OF HTML5
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270 ■ INDEX unsupported, 68 using
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284 ■ INDEX stopping Web Workers,
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Peter Lubbers - Pro HTML 5 Programming

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