20 Facts About JavaScript


JavaScript, often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS.

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JavaScript is a high-level, often just-in-time compiled language that conforms to the ECMAScript standard.

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JavaScript engines were originally used only in web browsers, but are now core components of some servers and a variety of applications.

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Choice of the JavaScript name has caused confusion, implying that it is directly related to Java.

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In 2005, Jesse James Garrett released a white paper in which he coined the term Ajax and described a set of technologies, of which JavaScript was the backbone, to create web applications where data can be loaded in the background, avoiding the need for full page reloads.

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Current JavaScript ecosystem has many libraries and frameworks, established programming practices, and substantial usage of JavaScript outside of web browsers.

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JavaScript engines are now embedded in a variety of other software systems, both for server-side website deployments and non-browser applications.

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JavaScript has recently begun to appear in some embedded systems, usually by leveraging Node.

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One partial exception is scoping: originally JavaScript only had function scoping with var; block scoping was added in ECMAScript 2015 with the keywords let and const.

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JavaScript is weakly typed, which means certain types are implicitly cast depending on the operation used.

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JavaScript has received criticism for the way it implements these conversions as the complexity of the rules can be mistaken for inconsistency.

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JavaScript functions are first-class; a function is considered to be an object.

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Variables in JavaScript can be defined using either the var, let or const keywords.

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In JavaScript, objects are usually created by creating an instance of a class.

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Common JavaScript-related security problem is cross-site scripting, a violation of the same-origin policy.

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In 2015, a JavaScript-based proof-of-concept implementation of a rowhammer attack was described in a paper by security researchers.

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In 2017, a JavaScript-based attack via browser was demonstrated that could bypass ASLR.

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Finally, Java did not support functional programming until Java 8, while JavaScript has done so from the beginning, being influenced by Scheme.

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JSON, or JavaScript Object Notation, is a general-purpose data interchange format that is defined as a subset of JavaScript's object literal syntax.

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JavaScript is the dominant client-side language of the Web, and many websites are script-heavy.

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