没有jQuery的$(document).ready等价

Question

我有一个使用的脚本$(document).ready,但它不使用jQuery中的任何其他内容.我想通过删除jQuery依赖项来减轻它.

如何在$(document).ready不使用jQuery的情况下实现自己的功能？我知道使用window.onload不会是相同的,因为window.onload在加载了所有图像,帧等之后的火灾.

Answer 1

有一个基于标准的替代品,DOMContentLoaded超过98%的浏览器支持,但不是IE8:

document.addEventListener("DOMContentLoaded", function(event) { 
  //do work
});

jQuery的本机函数比window.onload复杂得多,如下所示.

function bindReady(){
    if ( readyBound ) return;
    readyBound = true;

    // Mozilla, Opera and webkit nightlies currently support this event
    if ( document.addEventListener ) {
        // Use the handy event callback
        document.addEventListener( "DOMContentLoaded", function(){
            document.removeEventListener( "DOMContentLoaded", arguments.callee, false );
            jQuery.ready();
        }, false );

    // If IE event model is used
    } else if ( document.attachEvent ) {
        // ensure firing before onload,
        // maybe late but safe also for iframes
        document.attachEvent("onreadystatechange", function(){
            if ( document.readyState === "complete" ) {
                document.detachEvent( "onreadystatechange", arguments.callee );
                jQuery.ready();
            }
        });

        // If IE and not an iframe
        // continually check to see if the document is ready
        if ( document.documentElement.doScroll && window == window.top ) (function(){
            if ( jQuery.isReady ) return;

            try {
                // If IE is used, use the trick by Diego Perini
                // http://javascript.nwbox.com/IEContentLoaded/
                document.documentElement.doScroll("left");
            } catch( error ) {
                setTimeout( arguments.callee, 0 );
                return;
            }

            // and execute any waiting functions
            jQuery.ready();
        })();
    }

    // A fallback to window.onload, that will always work
    jQuery.event.add( window, "load", jQuery.ready );
}

Answer 2

编辑:

这是jQuery ready的可行替代品

function ready(callback){
    // in case the document is already rendered
    if (document.readyState!='loading') callback();
    // modern browsers
    else if (document.addEventListener) document.addEventListener('DOMContentLoaded', callback);
    // IE <= 8
    else document.attachEvent('onreadystatechange', function(){
        if (document.readyState=='complete') callback();
    });
}

ready(function(){
    // do something
});

取自 https://plainjs.com/javascript/events/running-code-when-the-document-is-ready-15/

另一个好的domReady功能来自/sf/answers/692979101/

由于接受的答案远非完整,我将jQuery.ready()基于jQuery 1.6.2源的"就绪"函数拼接在一起:

var ready = (function(){

    var readyList,
        DOMContentLoaded,
        class2type = {};
        class2type["[object Boolean]"] = "boolean";
        class2type["[object Number]"] = "number";
        class2type["[object String]"] = "string";
        class2type["[object Function]"] = "function";
        class2type["[object Array]"] = "array";
        class2type["[object Date]"] = "date";
        class2type["[object RegExp]"] = "regexp";
        class2type["[object Object]"] = "object";

    var ReadyObj = {
        // Is the DOM ready to be used? Set to true once it occurs.
        isReady: false,
        // A counter to track how many items to wait for before
        // the ready event fires. See #6781
        readyWait: 1,
        // Hold (or release) the ready event
        holdReady: function( hold ) {
            if ( hold ) {
                ReadyObj.readyWait++;
            } else {
                ReadyObj.ready( true );
            }
        },
        // Handle when the DOM is ready
        ready: function( wait ) {
            // Either a released hold or an DOMready/load event and not yet ready
            if ( (wait === true && !--ReadyObj.readyWait) || (wait !== true && !ReadyObj.isReady) ) {
                // Make sure body exists, at least, in case IE gets a little overzealous (ticket #5443).
                if ( !document.body ) {
                    return setTimeout( ReadyObj.ready, 1 );
                }

                // Remember that the DOM is ready
                ReadyObj.isReady = true;
                // If a normal DOM Ready event fired, decrement, and wait if need be
                if ( wait !== true && --ReadyObj.readyWait > 0 ) {
                    return;
                }
                // If there are functions bound, to execute
                readyList.resolveWith( document, [ ReadyObj ] );

                // Trigger any bound ready events
                //if ( ReadyObj.fn.trigger ) {
                //    ReadyObj( document ).trigger( "ready" ).unbind( "ready" );
                //}
            }
        },
        bindReady: function() {
            if ( readyList ) {
                return;
            }
            readyList = ReadyObj._Deferred();

            // Catch cases where $(document).ready() is called after the
            // browser event has already occurred.
            if ( document.readyState === "complete" ) {
                // Handle it asynchronously to allow scripts the opportunity to delay ready
                return setTimeout( ReadyObj.ready, 1 );
            }

            // Mozilla, Opera and webkit nightlies currently support this event
            if ( document.addEventListener ) {
                // Use the handy event callback
                document.addEventListener( "DOMContentLoaded", DOMContentLoaded, false );
                // A fallback to window.onload, that will always work
                window.addEventListener( "load", ReadyObj.ready, false );

            // If IE event model is used
            } else if ( document.attachEvent ) {
                // ensure firing before onload,
                // maybe late but safe also for iframes
                document.attachEvent( "onreadystatechange", DOMContentLoaded );

                // A fallback to window.onload, that will always work
                window.attachEvent( "onload", ReadyObj.ready );

                // If IE and not a frame
                // continually check to see if the document is ready
                var toplevel = false;

                try {
                    toplevel = window.frameElement == null;
                } catch(e) {}

                if ( document.documentElement.doScroll && toplevel ) {
                    doScrollCheck();
                }
            }
        },
        _Deferred: function() {
            var // callbacks list
                callbacks = [],
                // stored [ context , args ]
                fired,
                // to avoid firing when already doing so
                firing,
                // flag to know if the deferred has been cancelled
                cancelled,
                // the deferred itself
                deferred  = {

                    // done( f1, f2, ...)
                    done: function() {
                        if ( !cancelled ) {
                            var args = arguments,
                                i,
                                length,
                                elem,
                                type,
                                _fired;
                            if ( fired ) {
                                _fired = fired;
                                fired = 0;
                            }
                            for ( i = 0, length = args.length; i < length; i++ ) {
                                elem = args[ i ];
                                type = ReadyObj.type( elem );
                                if ( type === "array" ) {
                                    deferred.done.apply( deferred, elem );
                                } else if ( type === "function" ) {
                                    callbacks.push( elem );
                                }
                            }
                            if ( _fired ) {
                                deferred.resolveWith( _fired[ 0 ], _fired[ 1 ] );
                            }
                        }
                        return this;
                    },

                    // resolve with given context and args
                    resolveWith: function( context, args ) {
                        if ( !cancelled && !fired && !firing ) {
                            // make sure args are available (#8421)
                            args = args || [];
                            firing = 1;
                            try {
                                while( callbacks[ 0 ] ) {
                                    callbacks.shift().apply( context, args );//shifts a callback, and applies it to document
                                }
                            }
                            finally {
                                fired = [ context, args ];
                                firing = 0;
                            }
                        }
                        return this;
                    },

                    // resolve with this as context and given arguments
                    resolve: function() {
                        deferred.resolveWith( this, arguments );
                        return this;
                    },

                    // Has this deferred been resolved?
                    isResolved: function() {
                        return !!( firing || fired );
                    },

                    // Cancel
                    cancel: function() {
                        cancelled = 1;
                        callbacks = [];
                        return this;
                    }
                };

            return deferred;
        },
        type: function( obj ) {
            return obj == null ?
                String( obj ) :
                class2type[ Object.prototype.toString.call(obj) ] || "object";
        }
    }
    // The DOM ready check for Internet Explorer
    function doScrollCheck() {
        if ( ReadyObj.isReady ) {
            return;
        }

        try {
            // If IE is used, use the trick by Diego Perini
            // http://javascript.nwbox.com/IEContentLoaded/
            document.documentElement.doScroll("left");
        } catch(e) {
            setTimeout( doScrollCheck, 1 );
            return;
        }

        // and execute any waiting functions
        ReadyObj.ready();
    }
    // Cleanup functions for the document ready method
    if ( document.addEventListener ) {
        DOMContentLoaded = function() {
            document.removeEventListener( "DOMContentLoaded", DOMContentLoaded, false );
            ReadyObj.ready();
        };

    } else if ( document.attachEvent ) {
        DOMContentLoaded = function() {
            // Make sure body exists, at least, in case IE gets a little overzealous (ticket #5443).
            if ( document.readyState === "complete" ) {
                document.detachEvent( "onreadystatechange", DOMContentLoaded );
                ReadyObj.ready();
            }
        };
    }
    function ready( fn ) {
        // Attach the listeners
        ReadyObj.bindReady();

        var type = ReadyObj.type( fn );

        // Add the callback
        readyList.done( fn );//readyList is result of _Deferred()
    }
    return ready;
})();

如何使用:

<script>
    ready(function(){
        alert('It works!');
    });
    ready(function(){
        alert('Also works!');
    });
</script>

我不确定这段代码的功能如何,但它在我的表面测试中运行良好.这花了很长时间,所以我希望你和其他人可以从中受益.

PS.:我建议编译它.

或者您可以使用http://dustindiaz.com/smallest-domready-ever:

function r(f){/in/.test(document.readyState)?setTimeout(r,9,f):f()}
r(function(){/*code to run*/});

或者本机函数,如果你只需要支持新的浏览器(与jQuery ready不同,如果在页面加载后添加它,则不会运行)

document.addEventListener('DOMContentLoaded',function(){/*fun code to run*/})

Answer 3

三种选择:

1. 如果script是身体的最后一个标签时,DOM会前的脚本标记执行准备
2. 当DOM准备就绪时,"readyState"将变为"complete"
3. 将所有内容放在"DOMContentLoaded"事件侦听器下

的onreadystatechange

  document.onreadystatechange = function () {
     if (document.readyState == "complete") {
     // document is ready. Do your stuff here
   }
 }

资料来源:MDN

DOMContentLoaded

document.addEventListener('DOMContentLoaded', function() {
   console.log('document is ready. I can sleep now');
});

关注石器时代的浏览器: 转到jQuery源代码并使用该ready函数.在这种情况下,你没有解析+执行整个库,你只做了很小的一部分.

Answer 4

在结束标记之前放置您的<script>/*JavaScript code*/</script>权利. </body>

不可否认,这可能不适合每个人的目的,因为它需要更改HTML文件,而不是仅仅在JavaScript文件中执行某些操作document.ready,但仍然......

Answer 5

穷人的解决方案:

var checkLoad = function() {   
    document.readyState !== "complete" ? setTimeout(checkLoad, 11) : alert("loaded!");   
};  

checkLoad();  

查看小提琴

添加了这个,我想,自己的范围和非递归更好一点

(function(){
    var tId = setInterval(function() {
        if (document.readyState == "complete") onComplete()
    }, 11);
    function onComplete(){
        clearInterval(tId);    
        alert("loaded!");    
    };
})()

查看小提琴

Answer 6

我用这个:

document.addEventListener("DOMContentLoaded", function(event) { 
    //Do work
});

注意:这可能仅适用于较新的浏览器,尤其是:http://caniuse.com/#feat=domcontentloaded

Answer 7

2022版

2022 年，您所需要做的就是在脚本上添加 defer 属性，并将其加载到头部！

参考：https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#attr-defer

<!doctype html>
<html>
<head>
  <script src="/script.js" defer></script>
</head>
<body>

 <p>In 2022, all you need to do is put the defer attribute on your script, and load it in the head!</p>

</body>
</html>

Answer 8

真的,如果你只关心Internet Explorer 9+,这段代码就足以取代jQuery.ready:

    document.addEventListener("DOMContentLoaded", callback);

如果您担心Internet Explorer 6和一些非常奇怪且罕见的浏览器,这将起作用:

domReady: function (callback) {
    // Mozilla, Opera and WebKit
    if (document.addEventListener) {
        document.addEventListener("DOMContentLoaded", callback, false);
        // If Internet Explorer, the event model is used
    } else if (document.attachEvent) {
        document.attachEvent("onreadystatechange", function() {
            if (document.readyState === "complete" ) {
                callback();
            }
        });
        // A fallback to window.onload, that will always work
    } else {
        var oldOnload = window.onload;
        window.onload = function () {
            oldOnload && oldOnload();
            callback();
        }
    }
},

Answer 9

很久以前就问过这个问题了.对于任何刚看到这个问题的人来说,现在有一个名为"你可能不需要jquery"的网站 ,它按照所需的IE支持级别进行细分 - 所有jquery的功能,并提供了一些替代的,更小的库.

根据您的 IE8文档准备脚本可能不需要jquery

function ready(fn) {
    if (document.readyState != 'loading')
        fn();
    else if (document.addEventListener)
        document.addEventListener('DOMContentLoaded', fn);
    else
        document.attachEvent('onreadystatechange', function() {
            if (document.readyState != 'loading')
                fn();
        });
}

Answer 10

现在是 2020 年，<script>标签具有defer属性。

例如：

<script src="demo_defer.js" defer></script>

它指定在页面解析完成后执行脚本。

https://www.w3schools.com/tags/att_script_defer.asp

Answer 11

我最近在移动网站上使用它.这是John Resig的"Pro JavaScript Techniques"简化版.这取决于addEvent.

var ready = ( function () {
  function ready( f ) {
    if( ready.done ) return f();

    if( ready.timer ) {
      ready.ready.push(f);
    } else {
      addEvent( window, "load", isDOMReady );
      ready.ready = [ f ];
      ready.timer = setInterval(isDOMReady, 13);
    }
  };

  function isDOMReady() {
    if( ready.done ) return false;

    if( document && document.getElementsByTagName && document.getElementById && document.body ) {
      clearInterval( ready.timer );
      ready.timer = null;
      for( var i = 0; i < ready.ready.length; i++ ) {
        ready.ready[i]();
      }
      ready.ready = null;
      ready.done = true;
    }
  }

  return ready;
})();

Answer 12

jQuery的答案对我来说非常有用.通过一点点重构,它很好地满足了我的需求.我希望它可以帮助其他任何人.

function onReady ( callback ){
    var addListener = document.addEventListener || document.attachEvent,
        removeListener =  document.removeEventListener || document.detachEvent
        eventName = document.addEventListener ? "DOMContentLoaded" : "onreadystatechange"

    addListener.call(document, eventName, function(){
        removeListener( eventName, arguments.callee, false )
        callback()
    }, false )
}

Answer 13

跨浏览器(旧浏览器)和简单的解决方案:

var docLoaded = setInterval(function () {
    if(document.readyState !== "complete") return;
    clearInterval(docLoaded);

    /*
        Your code goes here i.e. init()
    */
}, 30);

在jsfiddle中显示警报

Answer 14

这是测试DOM就绪的最小代码片段,适用于所有浏览器(甚至是IE 8):

r(function(){
    alert('DOM Ready!');
});
function r(f){/in/.test(document.readyState)?setTimeout('r('+f+')',9):f()}

看到这个答案.

Answer 15

只需将其添加到HTML页面的底部即可...

<script>
    Your_Function();
</script>

因为,HTML文档是由上下解析的.

Answer 16

与 jQuery 相比，使用 JavaScript 等效项总是好的。原因之一是需要依赖的库少了，而且它们比 jQuery 等价物快得多。

http://youmightnotneedjquery.com/是 jQuery 等效项的一个很棒的参考。

就您的问题而言，我从上面的链接中获取了以下代码:) 唯一需要注意的是它仅适用于Internet Explorer 9及更高版本。

function ready(fn) {
    if (document.readyState != 'loading') {
        fn();
    }
    else {
        document.addEventListener('DOMContentLoaded', fn);
    }
}

Answer 17

值得一看的是Rock Solid addEvent（）和http://www.braksator.com/how-to-make-your-own-jquery。

这是网站关闭时的代码

function addEvent(obj, type, fn) {
    if (obj.addEventListener) {
        obj.addEventListener(type, fn, false);
        EventCache.add(obj, type, fn);
    }
    else if (obj.attachEvent) {
        obj["e"+type+fn] = fn;
        obj[type+fn] = function() { obj["e"+type+fn]( window.event ); }
        obj.attachEvent( "on"+type, obj[type+fn] );
        EventCache.add(obj, type, fn);
    }
    else {
        obj["on"+type] = obj["e"+type+fn];
    }
}

var EventCache = function(){
    var listEvents = [];
    return {
        listEvents : listEvents,
        add : function(node, sEventName, fHandler){
            listEvents.push(arguments);
        },
        flush : function(){
            var i, item;
            for(i = listEvents.length - 1; i >= 0; i = i - 1){
                item = listEvents[i];
                if(item[0].removeEventListener){
                    item[0].removeEventListener(item[1], item[2], item[3]);
                };
                if(item[1].substring(0, 2) != "on"){
                    item[1] = "on" + item[1];
                };
                if(item[0].detachEvent){
                    item[0].detachEvent(item[1], item[2]);
                };
                item[0][item[1]] = null;
            };
        }
    };
}();

// Usage
addEvent(window, 'unload', EventCache.flush);
addEvent(window, 'load', function(){alert("I'm ready");});

Answer 18

一旦 DOM 准备好，这个跨浏览器代码将调用一个函数：

var domReady=function(func){
    var scriptText='('+func+')();';
    var scriptElement=document.createElement('script');
    scriptElement.innerText=scriptText;
    document.body.appendChild(scriptElement);
};

它的工作原理如下：

1. 第一行domReady调用toString函数的方法来获取您传入的函数的字符串表示形式，并将其包装在立即调用该函数的表达式中。
2. 其余部分domReady使用表达式创建一个脚本元素并将其附加到body文档的 。
3. 浏览器运行bodyDOM 准备好后附加的脚本标签。

例如，如果您执行以下操作：domReady(function(){alert();});，则以下内容将附加到该body元素：

 <script>(function (){alert();})();</script>

请注意，这仅适用于用户定义的函数。以下内容将不起作用：domReady(alert);

Answer 19

最低限度和 100% 工作

我从PlainJS 中选择了答案，它对我来说很好用。它扩展DOMContentLoaded到所有浏览器都可以接受它。

这个函数相当于 jQuery 的$(document).ready()方法：

document.addEventListener('DOMContentLoaded', function(){
    // do something
});

但是，与 jQuery 相比，此代码只能在现代浏览器（IE > 8）中正确运行，并且在插入此脚本时文档已经呈现的情况下（例如通过 Ajax）则不会。因此，我们需要稍微扩展一下：

function run() {
    // do something
}

// in case the document is already rendered
if (document.readyState!='loading') run();
// modern browsers
else if (document.addEventListener) 
document.addEventListener('DOMContentLoaded', run);
// IE <= 8
else document.attachEvent('onreadystatechange', function(){
    if (document.readyState=='complete') run();
});

这基本上涵盖了所有可能性，并且是 jQuery 助手的可行替代品。