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Functions with promises also have promise aggregation methods that allow the program to await multiple promises at once or in some special pattern (such as C#'s Task.WhenAll(), [1]: 174–175 [13]: 664–665 which returns a valueless Task that resolves when all of the tasks in the arguments have resolved). Many promise types also have ...
The terms future, promise, delay, and deferred are often used interchangeably, although some differences in usage between future and promise are treated below. Specifically, when usage is distinguished, a future is a read-only placeholder view of a variable, while a promise is a writable, single assignment container which sets the value of the ...
A built-in Promise object provides functionality for handling promises and associating handlers with an asynchronous action's eventual result. Recently, the JavaScript specification introduced combinator methods, which allow developers to combine multiple JavaScript promises and do operations based on different scenarios.
Many dynamic languages, such as JavaScript, Lua, Python, Perl [1] [2] and PHP, allow a function object to be passed. CLI languages such as C# and VB.NET provide a type-safe encapsulating function reference known as delegate. Events and event handlers, as used in .NET languages, provide for callbacks.
JavaScript Object Notation (JSON) is often used as an alternative format for data interchange, [15] although other formats such as preformatted HTML or plain text can also be used. [16] A variety of popular JavaScript libraries, including JQuery, include abstractions to assist in executing Ajax requests.
JavaScript supports automatic semicolon insertion, meaning that semicolons that normally terminate a statement in C may be omitted in JavaScript. [16] Like C-style languages, control flow is done with the while, for, do / while, if / else, and switch statements. Functions are weakly typed and may accept and return any type.
Keith Clark's Selectivizr is a popular polyfill that makes many CSS3 selectors work in IE 8 and below. It reads the page's stylesheets looking for a number of known CSS3 selectors, then uses a JavaScript selector library to query the document for elements matching those selectors, applying the styles directly to those elements.
PythonMonkey uses SpiderMonkey to allow users to write programs where JavaScript and Python functions, types, and events interoperate and (where possible) share memory storage. [26] The text-based web browser ELinks uses SpiderMonkey to support JavaScript [27] Parts of SpiderMonkey are used in the Wine project's JScript (re-)implementation [28]