BOM（ Browser object model ） Mainly used to manage browser windows , It provides a lot of independent 、 Functions that can interact with browser windows , These features have nothing to do with any web content . Browser window window The object is BOM The top object of , Other objects are children of the object .

1.1 Use window object

window The object is BOM At the heart of , Represents an instance of a browser window . All variables and functions declared in the global scope are also window Properties and methods of objects .

1.1.1  Access browser window

adopt window Objects can be accessed in the browser window .

A brief description of the browser object is as follows ：

1.1.2 Global scope

client JavaScript The code runs in a global context ,window Object provides global scope .

The following usage ：

var a = ' I'm a programmer ';window.b = 'window.b';c = ' I like js';document.write(delete window.a);document.write(delete window.b);document.write(delete window.c + '<br>');document.write(window.a);document.write(window.b);document.write(window.c);

Use var Statement to declare global variables ,window For this property, a ‘configgurable’ Characteristics of .

1.1.3  Use system testing methods

window Object defines 3 Personal computer interaction Interface method ：

1.  alert()： Simple prompt dialog , Prompt information will pop up to users by browser . The method contains an optional prompt parameter .

2.  confirm()： Simple prompt dialog , Prompt information will pop up to users by browser . However, the dialog box that pops up with this method contains two buttons ,‘ confirm ’ and ‘ Cancel ’.

3.  prompt()： The prompt dialog box pops up , It can receive information from users , And return the user's input information to .

usage 1：

var user = prompt(' Please enter your user name :');if (!!user) {var ok = confirm(' The user name you entered is ：\n' + user + '\n Please make sure the .');if (ok) {document.write(' Welcome ：\n' + user);} else {user = prompt(' Please re-enter your user name :');document.write(' Welcome ：\n' + user);}} else {user = prompt(' Please enter your user name :');}

        this 3 Receive only plain text messages , Users can only use spaces 、 Line breaks and various symbols are used to format the displayed text in the prompt dialog box . Different browsers for this 3 The two dialog boxes display slightly different .

usage 2：

window.alert = function (title, info) {var box = document.getElementById('alert_box');var html = '<dl><dt>' + title + '</dt><dd>' + info + '</dd><\/dl>';if (box) {box.innerHTML = html;box.style.display = 'block';} else {var div = document.createElement('div');div.id = 'alert_box';div.style.display = 'block';document.body.appendChild(div);div.innerHTML = html;}}alert(' I'm a programmer ', ' I like Js!');

1.1.4 Control window position

        Use window Object's moveTo() and moveBy() Method can precisely move the window to a new location . These two methods take two parameters , among moveTo() It's in the new location x and y Coordinate value , and moveBy() Received is the number of pixels moving horizontally and vertically .

The following usage ：

window.moveTo(0, 0);window.moveBy(0, 100);window.moveTo(200, 300);window.moveBy(-50, 0);

1.1.5 Use timer

window Object contains 4 This is a timer specific method , Using them, you can run it at a bad time , Avoid continuous operation . You can design animation .

1. setTimeout() Method

Definition ：

setTimeout() Method is used to call functions or compute expressions after specified milliseconds. .

grammar ：

var o=setTimeout(code,millisec)

Parameters ：

The following usage ：

var o = document.getElementsByTagName('body')[0].childNodes;for (var i = 0; i < o.length; i++) {o[i].onmouseover = function (i) {return function () {f(o[i]);}}(i);}function f(o) {var out = setTimeout(function () {document.write(o.tagName);}, 500);}

2. clearTimeout() Method

Definition ：

clearTimeout() Method can be cancelled by setTimeout() Method set timeout.

grammar ：

clearTimeout(id_of_settimeout)

Parameters ：

id_of_settimeout（ from setTimeout() Back to ID value . This value identifies the block of deferred execution code to cancel .）

The following usage ：

var o = document.getElementsByTagName('body')[0].childNodes;for (var i = 0; i < o.length; i++) {o[i].onmouseover = function (i) {return function () {f(o[i]);}}(i);o[i].onmouseout = function (i) {return function () {clearTimeout(o[i].out);}}(i);}function f(o) {o.out = setTimeout(function () {document.write(o.tagName);}, 500);}

3. Setlnterval() Method

Definition ：

setInterval() Method according to the specified period （ In milliseconds ） To call a function or evaluate an expression .

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