The Brower Object Model (BOM) provides objects that interact with browser Windows independently of content. The core Object is Window.

A BOM is made up of a series of related objects, and each object provides a number of methods and attributes. But BOM lacks standards. ECMA is the standardisation body for JavaScript syntax, W3C is the standardisation body for DOM, and BOM was originally part of the Netscape browser standard.

The BOM provides many objects. These objects are used to access the browser and are called browser objects. The hierarchy of built-in objects is called the browser object model,

The structure of the BOM

As you can see from the figure, BOM is larger than DOM. It contains DOM (Doumemt). The core object of BOM is Window. The Window object is a top-level object of the browser. It plays a dual role as both an interface for JavaScript to access the browser window and a global object. Variables and functions defined in the global scope become properties and methods of the Window object. Example code is as follows:

<script>

// Variables in the global scope are properties of the window object
var num = 10;
console.log (num);
// Result is: 10
console.log (window.num);
// Result is: 10
// Global functions in the city are methods of the window object
function fn() {
console.log(11);
}
fn(); // Result: 11
window.fn();// Result: 11

</script>
Copy the code

In the previous section, you can also assign to an undeclared variable by omitting var because the variable is automatically converted to a property of the Window object. The previously learned alert() and prompt() methods belong to the window object and omit the preceding “window.” when called. Since the window object has a name attribute, it is not recommended to use name for variables declared in the global scope to avoid conflicts with the name attribute of the window object.

That’s the end of today’s introductory study

Peace

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