All global JavaScript objects, functions, and variables automatically become members of the window object. Constructor functions show you how to use constructor functions to define custom types in JavaScript. This is the preferred method used in libraries such as jQuery. The javascript objects are string, array, date etc. The method will not be available in objects where it is reimplemented, or on objects created using Object.create(null) (as these don't inherit from Object.prototype). The method will not be available in objects where it is reimplemented, or on objects created using Object.create(null) (as these don't inherit from Object.prototype). But more often is referred by old-school environment-specific names, such as window (browser) and global (Node.js). SWFObject is a small Javascript file used for embedding Adobe Flash content. What is the difference between Object.keys() and Object.entries() methods in JavaScript ? The method can be called on most JavaScript objects, because most objects descend from Object, and hence inherit its methods. Object.defineProperty(global, "window", { value: { location: { search: "test" } } }); In case window properties must be different in different tests, we can put window mocking into a function, and make it writable in order to override for different tests: var x= is a variable declaration. The Window object implements the WindowLocalStorage and WindowSessionStorage objects which has localStorage(window.localStorage) and sessionStorage(window.sessionStorage) properties respectively. JavaScript Window Events are associated with the windows object defined for describing the events. Note: if html document contains frame or iframe, browser creates additional window objects for each frame. But more often is referred by old-school environment-specific names, such as window (browser) and global (Node.js). Note: There is no public standard that applies to the Window object, but all major browsers support it. Note: There is no public standard that applies to the Window object, but all major browsers support it. The window object is supported by all browsers. If a document contain frames (