This chapter covers JavaScript libraries. It first explains what shims and polyfills are, two special kinds of libraries. Then it lists a few core libraries. Lastly, it points to additional library-related resources.
Shims and polyfills are libraries that retrofit newer functionality on older JavaScript engines:
A polyfill is a shim for a browser API. It typically checks if a browser supports an API. If it doesn’t, the polyfill installs its own implementation. That allows you to use the API in either case. The term polyfill comes from a home improvement product; according to Remy Sharp:
Polyfilla is a UK product known as Spackling Paste in the US. With that in mind: think of the browsers as a wall with cracks in it. These [polyfills] help smooth out the cracks and give us a nice smooth wall of browsers to work with.
Examples include:
The following libraries are quite established and close to the language. It is useful to be aware of them:
The ECMAScript Internationalization API is a standard JavaScript API that helps with tasks related to internationalization: collation (sorting and searching strings), number formatting, and date and time formatting. This section gives a brief overview and points you to more reading material.
The first edition of the API provides the following services:
Number formatting. Parameters include:
Date and time formatting. Parameters include:
Most of the functionality is accessed via an object in the global variable Intl, but the API also augments the following methods:
String.prototype.localeCompare
Number.prototype.toLocaleString
Date.prototype.toLocaleString
Date.prototype.toLocaleDateString
Date.prototype.toLocaleTimeString
The number of the standard “ECMAScript Internationalization API” (EIA) is ECMA-402. It is hosted by Ecma International, the association that also hosts EMCA-262, the ECMAScript language specification. Both standards are maintained by TC39. Therefore, EIA is as close to the language as you can get without being part of ECMA-262. The API has been designed to work with both ECMAScript 5 and ECMAScript 6. A set of conformance tests complements the standard and ensures that the various implementations of the API are compatible (ECMA-262 has a similar test suite).
Most modern browsers already support it or are in the process of supporting it. David Storey has created a detailed compatibility table (indicating which browsers support which locales and more).
The specification of the ECMAScript Internationalization API is edited by Norbert Lindenberg. It is available in PDF, HTML, and EPUB format. Additionally, there are several comprehensive introductory articles:
This section describes sites that collect information on JavaScript resources. There are several kinds of such directories.
Following is a list of general directories for JavaScript:
Specialized directories include:
Obviously, you can always directly browse the registries of package managers:
Directories for CDNs (content delivery networks) and CDN content include:
The following people contributed to this section: Kyle Simpson (@getify), Gildas Lormeau (@check_ca), Fredrik Sogaard (@fredrik_sogaard), Gene Loparco (@gloparco), Manuel Strehl (@m_strehl), and Elijah Manor (@elijahmanor).