BOM

The Browser Object Model (Browser Object Model) enables JavaScript to "talk" to the browser.

Browser Object Model (Browser Object Model) BOM provides objects that interact with the browser window independently of content. Since BOM is mainly used to manage communication between windows, its core object is window. BOM is composed of a series of related objects, and each object provides many methods and attributes. BOM lacks standards. The standardization organization for javaScript syntax is ECMA, the standardization organization for DOM is W3C.

(1), Window object

All browsers support the window object. It represents the browser window and is the top-level (core) object of the BOM. All objects are extended through her! All JavaScript global objects, functions, and variables are automatically members of the window object. Global variables are properties of the window object. Global functions are methods of the window object. Since the window object is a top-level object, you can specify the window object without displaying it when calling its sub-objects. For example, the following two lines of code are the same:

Document.write("The weather is really nice today"); window. document.write("The weather is really good today");

(2), window time waiting and interval function

Timer: It means that some events will be carried out after a human-set time trigger.

　1. One-time timer: only triggered once after the specified delay time. The setTimeout() method receives two parameters. The first parameter is the event to be triggered, and the second parameter is the specified time interval. Syntax: var t=setTimeout("javascript statement", milliseconds) Two ways to call the method:

setTimeout(showTime,1000);

setTimeout("showTime()",1000) ；

　2. Interval trigger timer: Triggered every certain time interval. The setInterval() method also receives two parameters. The first parameter is the event to be triggered, and the second parameter is the specified time interval. Syntax: var t=setInterval("javascript statement", milliseconds) Two ways to call the method:

setInterval(showTime,1000);

setInterval("showTime()",1000) ;

Cancel timer: Cancel the interaction time set by the timer.

　1. Cancel the one-time timer The clearTimeout(id) method receives an ID value returned by setTimeout(), which identifies the delayed execution code block to be canceled.

　2. Cancel the interval trigger timer The clearInterval(id) method receives an ID value returned by setInterval(), which identifies the interval execution code block to be canceled.

(3) Three system dialog boxes

alert(), confirm(), prompt()

　1.alert() is used to display a specified message and an alert box with an OK button.

　 2.confirm() is used to display a dialog box with a specified message and OK and Cancel buttons. Syntax: confirm(message) confirm() returns true if the user clicks the OK button. If the cancel button is clicked, confirm() returns false.

　3.prompt() is used to display a dialog box that prompts the user for input. Syntax: prompt(text,defaultText) text optional. Plain text to display in the dialog box. defaultText is optional. Default input text. Returns null if the user clicks the tooltip's cancel button. If the user clicks the confirm button, returns the currently displayed text of the input text box.

Tomorrow we will briefly talk about the sub-objects of window in BOM.

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