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An undefined variable in the source code of a computer program is a variable that is accessed in the code but has not been declared by that code. [1] In some programming languages, an implicit declaration is provided the first time such a variable is encountered at compile time. In other languages such a usage is considered to be sufficiently ...
A web worker, as defined by the World Wide Web Consortium (W3C) and the Web Hypertext Application Technology Working Group (WHATWG), is a JavaScript script executed from an HTML page that runs in the background, independently of scripts that may also have been executed from the same HTML page. [1]
In JavaScript, the empty string (""), null, undefined, NaN, +0, −0 and false [28] are sometimes called falsy (of which the complement is truthy) to distinguish between strictly type-checked and coerced Booleans (see also: JavaScript syntax#Type conversion). [29] As opposed to Python, empty containers (Arrays, Maps, Sets) are considered truthy.
A snippet of JavaScript code with keywords highlighted in different colors. The syntax of JavaScript is the set of rules that define a correctly structured JavaScript program. The examples below make use of the log function of the console object present in most browsers for standard text output.
Use of proprietary or undefined elements and attributes instead of those defined in W3C recommendations. For example the use of the Blink element or the Marquee element which were non-standard elements originally only supported by Netscape and Internet Explorer browsers respectively.
ESLint is a static code analysis tool for identifying problematic patterns found in JavaScript code. It was created by Nicholas C. Zakas in 2013. [2] [3] Rules in ESLint are configurable, and customized rules can be defined and loaded. ESLint covers both code quality and coding style issues.
A JavaScript function can check to see if a phone number is a valid format, i.e., is numeric, starts with a valid set of numbers ("0" for local, or an international dialing prefix followed by a valid country code) and is not too short to be a phone number. At first a JavaScript function is used to clear out any spacer characters.
Code can be modularized into functions defined with keyword function. PHP supports an optional object oriented coding style, with classes denoted by the class keyword. Functions defined inside classes are sometimes called methods. Control structures include: if, while, do/while, for, foreach, and switch. Statements are terminated by a semicolon ...