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Vue.js (commonly referred to as Vue; pronounced "view" [6]) is an open-source model–view–viewmodel front end JavaScript framework for building user interfaces and single-page applications. [12] It was created by Evan You and is maintained by him and the rest of the active core team members.
An undefined value must not be confused with empty string, Boolean "false" or other "empty" (but defined) values. Depending on circumstances, evaluation to an undefined value may lead to exception or undefined behaviour, but in some programming languages undefined values can occur during a normal, predictable course of program execution.
It was first used by Groovy 1.0 in 2007 [1] and is currently supported in languages such as C#, [2] Swift, [3] TypeScript, [4] Ruby, [5] Kotlin, [6] Rust, [7] JavaScript, [8] and others. There is currently no common naming convention for this operator, but safe navigation operator is the most widely used term.
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 ...
This is an accepted version of this page This is the latest accepted revision, reviewed on 13 February 2025. High-level programming language Not to be confused with Java (programming language), Javanese script, or ECMAScript. JavaScript Screenshot of JavaScript source code Paradigm Multi-paradigm: event-driven, functional, imperative, procedural, object-oriented Designed by Brendan Eich of ...
var x1 = 0; // A global variable, because it is not in any function let x2 = 0; // Also global, this time because it is not in any block function f {var z = 'foxes', r = 'birds'; // 2 local variables m = 'fish'; // global, because it wasn't declared anywhere before function child {var r = 'monkeys'; // This variable is local and does not affect the "birds" r of the parent function. z ...
This approach became popular thanks to JavaScript's increased use, its increase in client processing capabilities, and the trend to outsource computations to the client's web browser. Popular JavaScript templating libraries are AngularJS, Backbone.js, Ember.js, Handlebars.js, JSX (used by React), Vue.js and Mustache.js.
In particular, I made it possible to generate a new document by loading, e.g. javascript:'hello, world', but also (key for bookmarklets) to run arbitrary script against the DOM of the current document, e.g. javascript:alert(document.links[0].href). The difference is that the latter kind of URL uses an expression that evaluates to the undefined ...