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本文介紹了Javascript 將 URL 轉換為 BASE64 圖像的處理方法，對大家解決問題具有一定的參考價值，需要的朋友們下面隨著小編來一起學習吧！

問題描述

我正在構建一個 Ionic2 應用程序.我正在嘗試將圖像 url 轉換為 base64 圖像.我找到了我正在嘗試使用的 this.

我有以下代碼:

var imgUrl = 'https://www.google.de/images/srpr/logo11w.png';讓 base64image = this.getBase64Image(imgUrl);控制臺.log(base64image);

和

public getBase64Image(imgUrl) {var img = new Image();img.src = imgUrl;img.setAttribute('crossOrigin', '匿名');var canvas = document.createElement("canvas");canvas.width = img.width;canvas.height = img.height;var ctx = canvas.getContext("2d");ctx.drawImage(img, 0, 0);var dataURL = canvas.toDataURL("image/png");return dataURL.replace(/^data:image/(png|jpg);base64,/, "");}

但是，它會輸出以下內容:

<塊引用>

數據:，

我沒有收到任何錯誤，但需要的是 base64 圖像.

我的代碼一定不正確.誰能告訴我如何將 url 轉換為 base64 圖像?

謝謝

更新

感謝以下人員的反饋，我已按照他們的建議來加載圖像.現在我有以下代碼:

public getBase64Image(imgUrl): Promise{return new Promise<string>(resolve => {var img = new Image();img.src = imgUrl;img.setAttribute('crossOrigin', '匿名');img.onload = (() => {var canvas = document.createElement("canvas");canvas.width = img.width;canvas.height = img.height;var ctx = canvas.getContext("2d");ctx.drawImage(img, 0, 0);var dataURL = canvas.toDataURL("image/png");//console.log('UgetBase64Image.dataURL', dataURL);解析(dataURL.replace(/^data:image/(png|jpg);base64,/, ""));});});}

用法:

 let promise64: Promise;= this.getBase64Image(personModel.avatar);promise64.then((數據) => {personModel.avatar64 = 數據；});

當我運行 console.log 時，這似乎確實創建了一個 base64 圖像.

但是，我確實收到以下錯誤:

<塊引用>

錯誤:無法在HTMLCanvasElement"上執行toDataURL":可能無法導出受污染的畫布.在 HTMLImageElement.img.onload (utilityService.ts:80)

第 80 行:var dataURL = canvas.toDataURL("image/png");

我原以為以下代碼可以解決此安全問題，但無濟于事:

img.setAttribute('crossOrigin', 'anonymous');

更多信息:

完全錯誤:

 <代碼>:8100/iVBORw0KGgoAAAANSUhEUgAAAbgAAAG5CAYAAAD8liEWAAAgAElEQVR4Xty9B3NkR5Ksm ... bNkFj80enI0JnJ80 + gTsx2sbrX9zhp7k1oOOPZ5K7Oh/AvN0hP6tzZ6QAAAAAElFTkSuQmCC:1 GET HTTP://本地主機:8100/iVBORw0KGgoAAAANSUhEUgAAAbgAAAG5CAYAAAD8liEWAAAgAElEQ ... t3bNkFj80enI0JnJ80 + gTsx2sbrX9zhp7k1oOOPZ5K7Oh/AvN0hP6tzZ6QAAAAAElFTkSuQmCC凈:: ERR_EMPTY_RESPONSEpolyfills.js:3 POST http://localhost:8080/jbosswildfly-1.0/person/updatetime 400(錯誤請求)e@polyfills.js:3t.scheduleTask@polyfills.js:3e.scheduleMacroTask@polyfills.js:3(匿名)@ polyfills.js:3發送@VM9549:3(匿名)@xhr_backend.js:117Observable.subscribe@Observable.js:45MapOperator.call@map.js:54Observable.subscribe@Observable.js:42(匿名)@personService.ts:141t@polyfills.js:3PersonService.updateTimeStamps@personService.ts:140(匿名)@searchjobsParent.ts:109t.invoke@polyfills.js:3onInvoke@ng_zone.js:236t.invoke@polyfills.js:3onInvoke@ng_zone.js:236t.invoke@polyfills.js:3e.run@polyfills.js:3(匿名)@ polyfills.js:3t.invokeTask@polyfills.js:3onInvokeTask@ng_zone.js:227t.invokeTask@polyfills.js:3onInvokeTask@ng_zone.js:227t.invokeTask@polyfills.js:3e.runTask@polyfills.js:3我@polyfills.js:3polyfills.js:3 GET http://localhost:8080/jbosswildfly-1.0/person/list/favouritejob/null/0/400(錯誤請求)例外:無法在HTMLCanvasElement"上執行toDataURL":可能無法導出受污染的畫布.ErrorHandler.handleError@error_handler.js:47IonicErrorHandler.handleError @ ionic-error-handler.js:56下一個@application_ref.js:272schedulerFn @ async.js:82SafeSubscriber.__tryOrUnsub@Subscriber.js:223SafeSubscriber.next@Subscriber.js:172訂閱者._next @訂閱者.js:125訂閱者.next@訂閱者.js:89Subject.next@Subject.js:55EventEmitter.emit@async.js:74NgZone.triggerError @ ng_zone.js:278onHandleError @ ng_zone.js:257t.handleError @ polyfills.js:3e.runTask@polyfills.js:3調用@polyfills.js:3error_handler.js:52 原始堆棧跟蹤:ErrorHandler.handleError@error_handler.js:52IonicErrorHandler.handleError @ ionic-error-handler.js:56下一個@application_ref.js:272schedulerFn @ async.js:82SafeSubscriber.__tryOrUnsub@Subscriber.js:223SafeSubscriber.next@Subscriber.js:172訂閱者._next @訂閱者.js:125訂閱者.next@訂閱者.js:89Subject.next@Subject.js:55EventEmitter.emit@async.js:74NgZone.triggerError @ ng_zone.js:278onHandleError @ ng_zone.js:257t.handleError @ polyfills.js:3e.runTask@polyfills.js:3調用@polyfills.js:3error_handler.js:53 錯誤:無法在HTMLCanvasElement"上執行toDataURL":可能無法導出受污染的畫布.在 HTMLImageElement.img.onload (utilityService.ts:82)在 HTMLImageElement.n [as _onload] (polyfills.js:2)在 t.invokeTask (polyfills.js:3)在 Object.onInvokeTask (ng_zone.js:227)在 t.invokeTask (polyfills.js:3)在 e.runTask (polyfills.js:3)在 HTMLImageElement.invoke (polyfills.js:3)

解決方案

當圖像完全加載時，圖像實例會觸發 onload 事件.有了這個，另一個問題是處理異步函數.為了能夠使用 getBase64Image 使用的內容，必須使用回調函數.沒有回調函數，函數返回 undefined

讓 base64image = this.getBase64Image(imgUrl);控制臺.log(base64image);//不明確的

調整功能

public getBase64Image(imgUrl, callback) {var img = new Image();//onload 當圖像完全加載時觸發，并且具有寬度和高度img.onload = 函數(){var canvas = document.createElement("canvas");canvas.width = img.width;canvas.height = img.height;var ctx = canvas.getContext("2d");ctx.drawImage(img, 0, 0);var dataURL = canvas.toDataURL("image/png"),dataURL = dataURL.replace(/^data:image/(png|jpg);base64,/, "");回調(數據URL)；//base64 字符串};//設置屬性和srcimg.setAttribute('crossOrigin', '匿名');//img.src = imgUrl;}

用法:

this.getBase64Image(imgUrl, function(base64image){控制臺.log(base64image);});

I am building an Ionic2 app. I am trying to convert an image url to a base64 image. I have found this which I am trying to make use of.

I have the following code:

var imgUrl = 'https://www.google.de/images/srpr/logo11w.png';
let base64image = this.getBase64Image(imgUrl);
console.log(base64image);

and

public getBase64Image(imgUrl) {
    var img = new Image();
    img.src = imgUrl;
    img.setAttribute('crossOrigin', 'anonymous');
    var canvas = document.createElement("canvas");
    canvas.width = img.width;
    canvas.height = img.height;
    var ctx = canvas.getContext("2d");
    ctx.drawImage(img, 0, 0);
    var dataURL = canvas.toDataURL("image/png");
    return dataURL.replace(/^data:image/(png|jpg);base64,/, "");
}

But, it outputs the following:

data:,

I get no errors, but expect a base64 image.

My code must me incorrect. Can anyone please advise how to convert the url to a base64 image?

Thanks

UPDATE

Thank you to the feedback from the guys below, I have followed their advise to wit for the image to load. Now I have the following code:

public getBase64Image(imgUrl): Promise<string> {
    return new Promise<string>(resolve => {
        var img = new Image();
        img.src = imgUrl;
        img.setAttribute('crossOrigin', 'anonymous');
        img.onload = (() => {
            var canvas = document.createElement("canvas");
            canvas.width = img.width;
            canvas.height = img.height;
            var ctx = canvas.getContext("2d");
            ctx.drawImage(img, 0, 0);
            var dataURL = canvas.toDataURL("image/png");
            //console.log('UgetBase64Image.dataURL ', dataURL);
            resolve(dataURL.replace(/^data:image/(png|jpg);base64,/, ""));
        });
    });
}

usage:

                                let promise64: Promise<string> = this.getBase64Image(personModel.avatar);
                                promise64.then((data) => {
                                    personModel.avatar64 = data;

                                });

This does seem to create a base64 image when I run the console.log.

However, I do get the following error:

Error: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.
    at HTMLImageElement.img.onload (utilityService.ts:80)

Line 80: var dataURL = canvas.toDataURL("image/png");

I would have thought the following code would resolve this security issue, but to no avail:

img.setAttribute('crossOrigin', 'anonymous');

More info:

Full error:

:8100/iVBORw0KGgoAAAANSUhEUgAAAbgAAAG5CAYAAAD8liEWAAAgAElEQVR4Xty9B3NkR5Ksm…bNkFj80enI0JnJ80+gTsx2sbrX9zhp7k1oOOPZ5K7Oh/AvN0hP6tzZ6QAAAAAElFTkSuQmCC:1 GET http://localhost:8100/iVBORw0KGgoAAAANSUhEUgAAAbgAAAG5CAYAAAD8liEWAAAgAElEQ…t3bNkFj80enI0JnJ80+gTsx2sbrX9zhp7k1oOOPZ5K7Oh/AvN0hP6tzZ6QAAAAAElFTkSuQmCC net::ERR_EMPTY_RESPONSE
polyfills.js:3 POST http://localhost:8080/jbosswildfly-1.0/person/updatetime 400 (Bad Request)
e @ polyfills.js:3
t.scheduleTask @ polyfills.js:3
e.scheduleMacroTask @ polyfills.js:3
(anonymous) @ polyfills.js:3
send @ VM9549:3
(anonymous) @ xhr_backend.js:117
Observable.subscribe @ Observable.js:45
MapOperator.call @ map.js:54
Observable.subscribe @ Observable.js:42
(anonymous) @ personService.ts:141
t @ polyfills.js:3
PersonService.updateTimeStamps @ personService.ts:140
(anonymous) @ searchjobsParent.ts:109
t.invoke @ polyfills.js:3
onInvoke @ ng_zone.js:236
t.invoke @ polyfills.js:3
onInvoke @ ng_zone.js:236
t.invoke @ polyfills.js:3
e.run @ polyfills.js:3
(anonymous) @ polyfills.js:3
t.invokeTask @ polyfills.js:3
onInvokeTask @ ng_zone.js:227
t.invokeTask @ polyfills.js:3
onInvokeTask @ ng_zone.js:227
t.invokeTask @ polyfills.js:3
e.runTask @ polyfills.js:3
i @ polyfills.js:3
polyfills.js:3 GET http://localhost:8080/jbosswildfly-1.0/person/list/favouritejob/null/0/ 400 (Bad Request)

EXCEPTION: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.
ErrorHandler.handleError @ error_handler.js:47
IonicErrorHandler.handleError @ ionic-error-handler.js:56
next @ application_ref.js:272
schedulerFn @ async.js:82
SafeSubscriber.__tryOrUnsub @ Subscriber.js:223
SafeSubscriber.next @ Subscriber.js:172
Subscriber._next @ Subscriber.js:125
Subscriber.next @ Subscriber.js:89
Subject.next @ Subject.js:55
EventEmitter.emit @ async.js:74
NgZone.triggerError @ ng_zone.js:278
onHandleError @ ng_zone.js:257
t.handleError @ polyfills.js:3
e.runTask @ polyfills.js:3
invoke @ polyfills.js:3
error_handler.js:52 ORIGINAL STACKTRACE:
ErrorHandler.handleError @ error_handler.js:52
IonicErrorHandler.handleError @ ionic-error-handler.js:56
next @ application_ref.js:272
schedulerFn @ async.js:82
SafeSubscriber.__tryOrUnsub @ Subscriber.js:223
SafeSubscriber.next @ Subscriber.js:172
Subscriber._next @ Subscriber.js:125
Subscriber.next @ Subscriber.js:89
Subject.next @ Subject.js:55
EventEmitter.emit @ async.js:74
NgZone.triggerError @ ng_zone.js:278
onHandleError @ ng_zone.js:257
t.handleError @ polyfills.js:3
e.runTask @ polyfills.js:3
invoke @ polyfills.js:3
error_handler.js:53 Error: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.
    at HTMLImageElement.img.onload (utilityService.ts:82)
    at HTMLImageElement.n [as _onload] (polyfills.js:2)
    at t.invokeTask (polyfills.js:3)
    at Object.onInvokeTask (ng_zone.js:227)
    at t.invokeTask (polyfills.js:3)
    at e.runTask (polyfills.js:3)
    at HTMLImageElement.invoke (polyfills.js:3)

解決方案

Image instance fires onload event when the image is fully loaded. With this, another issue comes in which is dealing asynchronous functions. To be able to use what getBase64Image uses, a callback function must be used. Without a callback function, the function returns undefined

let base64image = this.getBase64Image(imgUrl);
console.log(base64image); // undefined

Adjusted function

public getBase64Image(imgUrl, callback) {

    var img = new Image();

    // onload fires when the image is fully loadded, and has width and height

    img.onload = function(){

      var canvas = document.createElement("canvas");
      canvas.width = img.width;
      canvas.height = img.height;
      var ctx = canvas.getContext("2d");
      ctx.drawImage(img, 0, 0);
      var dataURL = canvas.toDataURL("image/png"),
          dataURL = dataURL.replace(/^data:image/(png|jpg);base64,/, "");

      callback(dataURL); // the base64 string

    };

    // set attributes and src 
    img.setAttribute('crossOrigin', 'anonymous'); //
    img.src = imgUrl;

}

Usage:

this.getBase64Image(imgUrl, function(base64image){
     console.log(base64image);
});

這篇關于Javascript 將 URL 轉換為 BASE64 圖像的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！

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Javascript 將 URL 轉換為 BASE64 圖像

問題描述

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