Enumerable properties are those properties whose internal [[Enumerable]] flag is set to true, which is the default for properties created via simple assignment or via a property initializer (properties defined via Object.defineProperty and such default [[Enumerable]] to false). Enumerable properties show up in for...in loops unless the property's name is a Symbol. Ownership of properties is determined by whether the property belongs to the object directly and not to its prototype chain. Properties of an object can also be retrieved in total. There are a number of built-in means of detecting, iterating/enumerating, and retrieving object properties, with the chart showing which are available. Some sample code follows which demonstrates how to obtain the missing categories.

JavaScript

This part of the JavaScript section on MDN serves as a repository of facts about the JavaScript language. Read more about this reference.

JavaScript

The JavaScript reference serves as a repository of facts about the JavaScript language. The entire language is described here in detail. As you write JavaScript code, you'll refer to these pages often (thus the title "JavaScript reference"). If you're learning JavaScript, or need help understanding some of its capabilities or features, check out the JavaScript guide.

JavaScript

Errors, errors everywhere.

JavaScript

The decodeURI() function decodes a Uniform Resource Identifier (URI) previously created by encodeURI or by a similar routine.

JavaScript

The decodeURIComponent() function decodes a Uniform Resource Identifier (URI) component previously created by encodeURIComponent or by a similar routine.

JavaScript

The eval() function evaluates JavaScript code represented as a string.

JavaScript

The global Infinity property is a numeric value representing infinity.

JavaScript

The global isFinite() function determines whether the passed value is a finite number. If needed, the parameter is first converted to a number.

JavaScript

The isNaN() function determines whether a value is NaN or not. Note: coercion inside the isNaN function has interesting rules; you may alternatively want to use Number.isNaN(), as defined in ECMAScript 6, or you can use typeof to determine if the value is Not-A-Number.

JavaScript

The global NaN property is a value representing Not-A-Number.

JavaScript

The parseFloat() function parses a string argument and returns a floating point number.

JavaScript

The parseInt() function parses a string argument and returns an integer of the specified radix (the base in mathematical numeral systems).

JavaScript

The global undefined property represents the primitive value undefined. It is one of JavaScript's primitive types.

JavaScript

The uneval() function creates a string representation of the source code of an Object.

JavaScript

JavaScript

JavaScript

JavaScript has a concurrency model based on an "event loop". This model is quite different from models in other languages like C and Java.

Advanced JavaScript

This chapter discusses JavaScript's basic grammar, variable declarations, data types and literals.

Guide JavaScript

This chapter introduces JavaScript and discusses some of its fundamental concepts.

Guide JavaScript