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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 ...
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]
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.
CommonJS's specification of how modules should work is widely used today for server-side JavaScript with Node.js. [1] It is also used for browser-side JavaScript, but that code must be packaged with a transpiler since browsers don't support CommonJS. [1]
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. [19]
The webpage can be modified by JavaScript to dynamically display (and allow the user to interact with) the new information. The built-in XMLHttpRequest object is used to execute Ajax on webpages, allowing websites to load content onto the screen without refreshing the page. Ajax is not a new technology, nor is it a new language.