downloadjs下载库 源码解析_jsdownload

downloadjs github地址

判断环境

(function (root, factory) {
	if (typeof define === 'function' && define.amd) {
		// AMD. Register as an anonymous module.
		define([], factory);
	} else if (typeof exports === 'object') {
		// Node. Does not work with strict CommonJS, but
		// only CommonJS-like environments that support module.exports,
		// like Node.
		module.exports = factory();
	} else {
		// Browser globals (root is window)
		root.download = factory();
  }
}(this, function () {
	//...
}
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初始化

(function (root, factory) {
	//...
}(this, function () {
	return function download(data, strFileName, strMimeType) {

		var self = window, // this script is only for browsers anyway...
			defaultMime = "application/octet-stream", // this default mime also triggers iframe downloads
			mimeType = strMimeType || defaultMime,
			payload = data,
			// 只传第一个参数，说明通过url下载，否则是下载指定内容
			url = !strFileName && !strMimeType && payload,
			// 默认通过a标签进行下载
			anchor = document.createElement("a"),
			toString = function(a){return String(a);},
			// 默认将下载内容转换成blob
			myBlob = (self.Blob || self.MozBlob || self.WebKitBlob || toString),
			fileName = strFileName || "download",
			blob,
			reader;
			myBlob= myBlob.call ? myBlob.bind(self) : Blob ;
		}
		
		if(String(this)==="true"){ //reverse arguments, allowing download.bind(true, "text/xml", "export.xml") to act as a callback
			payload=[payload, mimeType];
			mimeType=payload[0];
			payload=payload[1];
		}

		//...
})
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统一的下载方法

function saver(url, winMode){
     // 默认通过a标签的 download 进行下载
	if ('download' in anchor) { //html5 A[download]
		anchor.href = url;
		anchor.setAttribute("download", fileName);
		anchor.className = "download-js-link";
		anchor.innerHTML = "downloading...";
		anchor.style.display = "none";
		document.body.appendChild(anchor);
		setTimeout(function() {
			anchor.click();
			document.body.removeChild(anchor);
			// 浏览器window环境 URL.revokeObjectURL 释放资源
			if(winMode===true){setTimeout(function(){ self.URL.revokeObjectURL(anchor.href);}, 250 );}
		}, 66);
		return true;
	}
	
    // 如果不支持a标签下载，通过location.href下载，但只能下载.rar、.exe这种浏览器无法直接打开的包，否则浏览器将直接打开文件
	// handle non-a[download] safari as best we can:
	if(/(Version)\/(\d+)\.(\d+)(?:\.(\d+))?.*Safari\//.test(navigator.userAgent)) {
	
		// data url的格式统一改成'application/octet-stream'，表示浏览器不用知道是什么类型，只知道是二进制文件，触发下载行为
		if(/^data:/.test(url))	url="data:"+url.replace(/^data:([\w\/\-\+]+)/, defaultMime);
		
		//window.open不行就使用confirm打开页面下载
		if(!window.open(url)){ // popup blocked, offer direct download:
			if(confirm("Displaying New Document\n\nUse Save As... to download, then click back to return to this page.")){ location.href=url; }
		}
		return true;
	}

	// 老版本谷歌+火狐通过iframe下载
	//do iframe dataURL download (old ch+FF):
	var f = document.createElement("iframe");
	document.body.appendChild(f);

	if(!winMode && /^data:/.test(url)){ // force a mime that will download:
		url="data:"+url.replace(/^data:([\w\/\-\+]+)/, defaultMime);
	}
	f.src=url;
	setTimeout(function(){ document.body.removeChild(f); }, 333);

}//end saver
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下载给定内容

• 下载字符串等格式

(function (root, factory) {
	//...
}(this, function () {
	return function download(data, strFileName, strMimeType) {
		// ...
		
		//将传递的data转换成blob格式，以及判断传递的data是否已经是blob
		blob = payload instanceof myBlob ?
			payload :
			new myBlob([payload], {type: mimeType}) ;
			
		//兼容ie10+
		if (navigator.msSaveBlob) { // IE10+ : (has Blob, but not a[download] or URL)
			return navigator.msSaveBlob(blob, fileName);
		}
		
		// 将blob转化成blob url
		if(self.URL){ // simple fast and modern way using Blob and URL:
			// 将blob data内容变成blob url
			saver(self.URL.createObjectURL(blob), true);
		}else{
			// handle non-Blob()+non-URL browsers:
			// 如果不支持winodw.Blob,手动转换成base64格式
			if(typeof blob === "string" || blob.constructor===toString ){
				try{
					return saver( "data:" +  mimeType   + ";base64,"  +  self.btoa(blob)  );
				}catch(y){
					return saver( "data:" +  mimeType   + "," + encodeURIComponent(blob)  );
				}
			}
			
			// 支持blob但是不支持window.URL，通过FileReader转换成Blob url 
			// Blob but not URL support:
			reader=new FileReader();
			reader.onload=function(e){
				saver(this.result);
			};
			reader.readAsDataURL(blob);
		}
		return true
	}
}));
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• 下载base64格式

(function (root, factory) {
	//...
}(this, function () {
	return function download(data, strFileName, strMimeType) {
		// ...
		
		// 当传入的是base64
		//go ahead and download dataURLs right away
		if(/^data:([\w+-]+\/[\w+.-]+)?[,;]/.test(payload)){
		
			if(payload.length > (1024*1024*1.999) && myBlob !== toString ){
			    // 转换成blob
				payload=dataUrlToBlob(payload);
				mimeType=payload.type || defaultMime;
			}else{
				// 兼容ie10			
				return navigator.msSaveBlob ?  // IE10 can't do a[download], only Blobs:
					navigator.msSaveBlob(dataUrlToBlob(payload), fileName) :
					saver(payload) ; // everyone else can save dataURLs un-processed
			}
			
		}else{//not data url, is it a string with special needs?
			 // 匹配中文字符等特殊字符，这里判定成特殊字符串，即下载内容是该字符串
			if(/([\x80-\xff])/.test(payload)){			  
				var i=0, tempUiArr= new Uint8Array(payload.length), mx=tempUiArr.length;
				for(i;i<mx;++i) tempUiArr[i]= payload.charCodeAt(i);
			 	payload=new myBlob([tempUiArr], {type: mimeType});
			}		  
		}
		
		function dataUrlToBlob(strUrl) {
		    // 这里使用正则split
			var parts= strUrl.split(/[:;,]/),
			//'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAHgAAAB4CAMAAAAOusbgAAAAeFBMVEUAwAD///+U5ZTc9twOww7G8MYwzDCH4=='.split(/[:;,]/)
			//['data', 'image/png', 'base64', 'iVBORw0KGgoAAAANSUhEUgAAAHgAAAB4CAMAAAAOusbgAAAAeFBMVEUAwAD///+U5ZTc9twOww7G8MYwzDCH4==']
			type= parts[1],
			// base64使用atob进行解码
			decoder= parts[2] == "base64" ? atob : decodeURIComponent,
			binData= decoder( parts.pop() ),
			mx= binData.length,
			i= 0,
			uiArr= new Uint8Array(mx);

			for(i;i<mx;++i) uiArr[i]= binData.charCodeAt(i);

			return new myBlob([uiArr], {type: type});
	  }
		
	  	// 接下来的流程和下载字符串一致
		blob = payload instanceof myBlob ?
			payload :
			new myBlob([payload], {type: mimeType}) ;	
	  
	}
})
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• 下载blob格式

(function (root, factory) {
	//...
}(this, function () {
	return function download(data, strFileName, strMimeType) {
		// ...
		
		//将传递的data转换成blob格式，以及判断传递的data是否已经是blob
		blob = payload instanceof myBlob ?
			payload :
			new myBlob([payload], {type: mimeType}) ;
		//接下来和字符串转换成blob格式后下载一致
		//...
	}
})
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通过url下载

(function (root, factory) {
	//...
}(this, function () {
	return function download(data, strFileName, strMimeType) {
		//...
		
		// 如果第一参数传递的是url
		if(url && url.length< 2048){ // if no filename and no mime, assume a url was passed as the only argument
			fileName = url.split("/").pop().split("?")[0];
			anchor.href = url; // assign href prop to temp anchor
			//通过浏览器标签去校验是否url是否合法，骚操作
		  	if(anchor.href.indexOf(url) !== -1){ // if the browser determines that it's a potentially valid url path:
				//通过ajax发起下载请求，返回blob二进制流
        		var ajax=new XMLHttpRequest();
        		ajax.open( "GET", url, true);
        		ajax.responseType = 'blob';
        		ajax.onload= function(e){
				  //此时传入的是二进制,递归调用download,走下载二进制流的逻辑
				  download(e.target.response, fileName, defaultMime);
				};
        		setTimeout(function(){ ajax.send();}, 0); // allows setting custom ajax headers using the return:
			    return ajax;
			} // end if valid url?
		} // end if url?
	
	}
})
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