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If the parameter is not a promise, the parameter itself will be returned immediately. [21] Many libraries provide promise objects that can also be used with await, as long as they match the specification for native JavaScript promises. However, promises from the jQuery library were not Promises/A+ compatible until jQuery 3.0. [22]
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.
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.
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.
Ember was an adopter of standards around JavaScript and the web, including promises, web components and ES6 syntax. [ 17 ] [ 18 ] Yehuda Katz, one of Ember's co-founders, is a member on TC39, which is the committee responsible for future versions of the JavaScript language.
ReactiveX (Rx, also known as Reactive Extensions) is a software library originally created by Microsoft that allows imperative programming languages to operate on sequences of data regardless of whether the data is synchronous or asynchronous.