原生javascript實現非同步的7種方式
原生的javascript 實現非同步的方式其實遠遠不至7種,
大可以分3類,
延遲型別:setTimeout(setInterval也是可以的)、requestAnimationFrame、setImmediate(IE10及以上)
監聽事件實現的型別:監聽new Image載入狀態、監聽script載入狀態、監聽iframe載入狀態、Message
帶有非同步功能型別 Promise、ajax( XMLHttpRequest、ActiveXObject)、Worker;
考慮到
1.iframe 效率過慢;
2.ajax 在ie下一定要載入真實的檔案才能觸發open及send;
3.Worker 雖然具有非同步特性,但它屬於多執行緒的範疇,需要將主要的演算法寫在單獨的js檔案中才能完整體現其優點,若單單為了非同步化而使用的話太浪費了。
所有這3種方式就不列出。
一、實現非同步的方式
1.setTimeout
2.setImmediate
3.requestAnimationFrame
4.監聽new Image載入狀態
5.監聽script載入狀態
6.Message
7.Promise
setTimeout
這個是最簡單的
setTimeout( function() {
console.log(1);
});
console.log(2);
setImmediate
IE10新增的新功能,專門用於解放ui執行緒。IE10以下及其他瀏覽器不支援
setImmediate(function(){
console. log(1);
});
console.log(2);
requestAnimationFrame
HTML5/CSS3時代新產物,專門用於動畫。低階瀏覽器不支援
var asynByAniFrame = (function(){
var _window = window,
frame = _window.requestAnimationFrame
|| _window.webkitRequestAnimationFrame
|| _window.mozRequestAnimationFrame
|| _window. oRequestAnimationFrame
|| _window.msRequestAnimationFrame;
return function( callback ) { frame( callback ) };
})();
asynByAniFrame(function(){
console.log(1);
})
console.log(2);
監聽new Image載入狀態實現
通過載入一個data:image資料格式的圖片,並監聽器載入狀態實現非同步。
儘管部分瀏覽器不支援data:image圖片資料格式,但仍然可以觸發其onerror狀態實現非同步,但IE8及以下對data:image資料格式的圖片,onerror為同步執行
function asynByImg( callback ) {
var img = new Image();
img.onload = img.onerror = img.onreadystatechange = function() {
img = img.onload = img.onerror = img.onreadystatechange = null;
callback();
}
img.src = "data:image/png,";
}
asynByImg(function(){
console.log(1);
});
console.log(2);
監聽script載入狀態實現
原理同new Image是一樣的,生成一個data:text/javascript的script,並監聽其載入狀態實現非同步。
儘管部分瀏覽器不支援data:text/javascript格式資料的script,但仍然可以觸發其onerror、onreadystatechange事件實現非同步。
var asynByScript = (function() {
var _document = document,
_body = _document.body,
_src = "data:text/javascript,",
//非同步佇列
queue = [];
return function( callback ) {
var script = _document.createElement("script");
script.src = _src;
//新增到佇列
queue[ queue.length ] = callback;
script.onload = script.onerror = script.onreadystatechange = function () {
script.onload = script.onerror = script.onreadystatechange = null;
_body.removeChild( script );
script = null;
//執行並刪除佇列中的第一個
queue.shift()();
};
_body.appendChild( script );
}
})();
asynByScript( function() {
console.log(1);
} );
console.log(2);
Message
html5新技能,通過監聽window.onmessage事件實現,然後postMessage傳送訊息,觸發onmessage事件實現非同步
var asynByMessage = (function() {
//非同步佇列
var queue = [];
window.addEventListener('message', function (e) {
//只響應asynByMessage的召喚
if ( e.data === 'asynByMessage' ) {
e.stopPropagation();
if ( queue.length ) {
//執行並刪除佇列中的第一個
queue.shift()();
}
}
}, true);
return function( callback ) {
//新增到佇列
queue[ queue.length ] = callback;
window.postMessage('asynByMessage', '*');
};
})();
asynByMessage(function() {
console.log(1);
});
console.log(2);
Promise
ES6的新技能,具有非同步性質
var asynByPromise = (function() {
var promise = Promise.resolve({
then : function( callback ) {
callback();
}
});
return function( callback ) {
promise.then(function(){
callback();
})
};
})();
asynByPromise(function() {
console.log(1);
});
console.log(2);
二、各種非同步方式的執行效率
測試程式碼
/**
* 檢驗一個方法是否瀏覽器原生
* @param { Function } func 需檢測的方法
* @return { Boolean } 是否瀏覽器原生
*/
function isNativeFunc( func ) {
return typeof func === 'function' && /^[^{]+\{\s*\[native \w/.test( func );
}
var _window = window,
frame = _window.requestAnimationFrame
|| _window.webkitRequestAnimationFrame
|| _window.mozRequestAnimationFrame
|| _window.oRequestAnimationFrame
|| _window.msRequestAnimationFrame;
_window = null;
var asynByPromise = isNativeFunc( window.Promise ) && (function() {
var promise = Promise.resolve({
then : function( callback ) {
callback();
}
});
return function( callback ) {
promise.then(function(){
callback();
})
};
})();
var asynByAniFrame = isNativeFunc( frame ) && function( callback ) {
frame( callback );
};
var asynByWorker = (function() {
//生成一個新執行緒
var worker = new Worker('asynWorker.js'),
queue = [];
//監聽執行緒
worker.addEventListener('message', function (e) {
//處理結果
queue.shift()();
}, true);
return function( callback ) {
queue[ queue.length ] = callback;
worker.postMessage('');
};
})();
var asynByMessage = isNativeFunc( window.postMessage ) && (function() {
//非同步佇列
var queue = [];
window.addEventListener('message', function (e) {
//只響應asynByMessage的召喚
if ( e.data === 'asynByMessage' ) {
e.stopPropagation();
if ( queue.length ) {
//執行並刪除佇列中的第一個
queue.shift()();
}
}
}, true);
return function( callback ) {
//新增到佇列
queue[ queue.length ] = callback;
window.postMessage('asynByMessage', '*');
};
})();
function asynByImg( callback ) {
var img = new Image();
img.onload = img.onerror = img.onreadystatechange = function() {
img = img.onload = img.onerror = img.onreadystatechange = null;
callback();
}
img.src = "data:image/png,";
}
//是否支援圖片非同步方式
var supAsynImg = true;
asynByImg(function(){
//IE8及以下對data:image資料格式的圖片,onerror為同步執行
supAsynImg = false;
})
var asynByScript = (function() {
var _document = document,
_body = _document.body,
_src = "data:text/javascript,",
//非同步佇列
queue = [];
return function( callback ) {
var script = _document.createElement("script");
script.src = _src;
//新增到佇列
queue[ queue.length ] = callback;
script.onload = script.onerror = script.onreadystatechange = function () {
script.onload = script.onerror = script.onreadystatechange = null;
_body.removeChild( script );
script = null;
//執行並刪除佇列中的第一個
queue.shift()();
};
_body.appendChild( script );
}
})();
function asynBySetImmediate( callback ) {
setImmediate( callback );
}
setTimeout(function() {
console.log('setTimeout');
});
if ( supAsynImg ) {
asynByImg(function() {
console.log('asynByImg');
});
}
asynByScript(function() {
console.log('asynByScript');
});
if ( isNativeFunc( window.setImmediate) ) {
asynBySetImmediate(function() {
console.log('asynBySetImmediate');
});
}
if (isNativeFunc( window.Promise )) {
asynByPromise(function() {
console.log('asynByPromise');
});
}
if ( isNativeFunc( frame ) ) {
asynByAniFrame(function() {
console.log('asynByAniFrame');
});
}
if ( isNativeFunc( window.postMessage ) ) {
asynByMessage(function() {
console.log('asynByMessage');
});
}
asynByWorker(function() {
console.log('asynByWorker');
});
按照這樣的結果,其實留下4個就夠了
高階瀏覽器
支援promise的時候 asynByPromise 最快
支援requestAnimationFrame的時候 比 promise 慢,比其他快
其他瀏覽器
支援data:image資料格式圖片非同步的,asynByImg 比 asynScript快
每個瀏覽器都支援 data:text/javascript 資料格式的非同步方式
所以
asynByPromise > asynByAniFrame > asynByImg > asynByScript
奇怪的是,IE中 setImmediate 從來沒跑贏過 setTimeout。
三、最終程式碼
/**
* 檢驗一個方法是否瀏覽器原生
* @param { Function } func 需檢測的方法
* @return { Boolean } 是否瀏覽器原生
*/
function isNativeFunc( func ) {
return typeof func === 'function' && /^[^{]+\{\s*\[native \w/.test( func );
}
var _window = window,
frame = _window.requestAnimationFrame
|| _window.webkitRequestAnimationFrame
|| _window.mozRequestAnimationFrame
|| _window.oRequestAnimationFrame
|| _window.msRequestAnimationFrame,
//是否支援圖片非同步方式
supAsynImg = true;
_window = null;
function asynByImg( callback ) {
var img = new Image();
img.onload = img.onerror = img.onreadystatechange = function() {
img = img.onload = img.onerror = img.onreadystatechange = null;
callback();
}
img.src = "data:image/png,";
}
asynByImg(function(){
//IE8及以下對data:image資料格式的圖片,onerror為同步執行
supAsynImg = false;
});
var asynFire =
//瀏覽器中有Promise方法且為原生
isNativeFunc( window.Promise )
&&
(function() {
var promise = Promise.resolve({
then : function( callback ) {
callback();
}
});
return function( callback ) {
promise.then(function(){
callback();
})
};
})()
||
//瀏覽器中有requestAnimationFrame方法且為原生
isNativeFunc( frame )
&&
function( callback ) {
frame( callback );
}
||
//支援圖片非同步
supAsynImg
&&
asynByImg
||
//script非同步
(function() {
var _document = document,
_body = _document.body,
_src = "data:text/javascript,",
//非同步佇列
queue = [];
return function( callback ) {
var script = _document.createElement("script");
script.src = _src;
//新增到佇列
queue[ queue.length ] = callback;
script.onload = script.onerror = script.onreadystatechange = function () {
script.onload = script.onerror = script.onreadystatechange = null;
_body.removeChild( script );
script = null;
//執行並刪除佇列中的第一個
queue.shift()();
};
_body.appendChild( script );
}
})();
if ( asynFire !== asynByImg ) {
asynByImg = null;
}