当我挑战学习15小时

Firefox 15 shipped on August 28, 2012. This article lists key changes that are useful for not only Web developers to know about, but also Firefox and Gecko developers as well as add-on developers.

The [Symbol.iterator]() method of Segments instances implements the iterable protocol and allows Segments objects to be consumed by most syntaxes expecting iterables, such as the spread syntax and for...of loops. It returns a segments iterator object that yields data about each segment.

HTML is designed with extensibility in mind for data that should be associated with a particular element but need not have any defined meaning. data-* attributes allow us to store extra information on standard, semantic HTML elements without other hacks such as non-standard attributes, or extra properties on DOM.

The HTML element represents tabular data—that is, information presented in a two-dimensional table comprised of rows and columns of cells containing data.

Perhaps more exciting than just fills and strokes is the fact that you can also create and apply gradients as either fills or strokes.

The parseInt() function parses a string argument and returns an integer of the specified radix (the base in mathematical numeral systems).

The reduce() method of Array instances executes a user-supplied "reducer" callback function on each element of the array, in order, passing in the return value from the calculation on the preceding element. The final result of running the reducer across all elements of the array is a single value.

The sort() method of Array instances sorts the elements of an array in place and returns the reference to the same array, now sorted. The default sort order is ascending, built upon converting the elements into strings, then comparing their sequences of UTF-16 code unit values.

Along with every request to a server, browsers include a User-Agent HTTP header with a value called a user agent (UA) string. This string is intended to identify the browser, its version number, and its host operating system.

This document describes the user agent string used in Firefox 4 and later and applications based on Gecko 2.0 and later. For a breakdown of changes to the string in Gecko 2.0, see Final User Agent string for Firefox 4 (blog post). See also this document on user agent sniffing and this Hacks blog post.