我需要将我的图像转换为Base64字符串，这样我就可以将我的图像发送到服务器。
有JavaScript文件吗?否则，我如何转换它?
当前回答
我发现最安全可靠的方法是使用FileReader()。
演示:映像到Base64
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
</head>
<body>
<input id="myinput" type="file" onchange="encode();" />
<div id="dummy">
</div>
<div>
<textarea style="width:100%;height:500px;" id="txt">
</textarea>
</div>
<script>
function encode() {
var selectedfile = document.getElementById("myinput").files;
if (selectedfile.length > 0) {
var imageFile = selectedfile[0];
var fileReader = new FileReader();
fileReader.onload = function(fileLoadedEvent) {
var srcData = fileLoadedEvent.target.result;
var newImage = document.createElement('img');
newImage.src = srcData;
document.getElementById("dummy").innerHTML = newImage.outerHTML;
document.getElementById("txt").value = document.getElementById("dummy").innerHTML;
}
fileReader.readAsDataURL(imageFile);
}
}
</script>
</body>
</html>
更新-相同的代码与评论@AnniekJ请求:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
</head>
<body>
<input id="myinput" type="file" onchange="encode();" />
<div id="dummy">
</div>
<div>
<textarea style="width:100%;height:500px;" id="txt">
</textarea>
</div>
<script>
function encode() {
// Get the file objects that was selected by the user from myinput - a file picker control
var selectedfile = document.getElementById("myinput").files;
// Check that the user actually selected file/s from the "file picker" control
// Note - selectedfile is an array, hence we check it`s length, when length of the array
// is bigger than 0 than it means the array containes file objects
if (selectedfile.length > 0) {
// Set the first file object inside the array to this variable
// Note: if multiple files are selected we can itterate on all of the selectedfile array using a for loop - BUT in order to not make this example complicated we only take the first file object that was selected
var imageFile = selectedfile[0];
// Set a filereader object to asynchronously read the contents of files (or raw data buffers) stored on the user's computer, using File or Blob objects to specify the file or data to read.
var fileReader = new FileReader();
// We declare an event of the fileReader class (onload event) and we register an anonimous function that will be executed when the event is raised. it is "trick" we preapare in order for the onload event to be raised after the last line of this code will be executed (fileReader.readAsDataURL(imageFile);) - please read about events in javascript if you are not familiar with "Events"
fileReader.onload = function(fileLoadedEvent) {
// AT THIS STAGE THE EVENT WAS RAISED
// Here we are getting the file contents - basiccaly the base64 mapping
var srcData = fileLoadedEvent.target.result;
// We create an image html element dinamically in order to display the image
var newImage = document.createElement('img');
// We set the source of the image we created
newImage.src = srcData;
// ANOTHER TRICK TO EXTRACT THE BASE64 STRING
// We set the outer html of the new image to the div element
document.getElementById("dummy").innerHTML = newImage.outerHTML;
// Then we take the inner html of the div and we have the base64 string
document.getElementById("txt").value = document.getElementById("dummy").innerHTML;
}
// This line will raise the fileReader.onload event - note we are passing the file object here as an argument to the function of the event
fileReader.readAsDataURL(imageFile);
}
}
</script>
</body>
</html>
其他回答
需要利用读取器将blob转换为base64，更喜欢使用async-await语法，所以我选择提取读取器逻辑到帮助器，像这样:
//* Convert resBlob to base64
export const blobToData = (blob: Blob) => {
return new Promise((resolve) => {
const reader = new FileReader()
reader.onloadend = () => resolve(reader.result)
reader.readAsDataURL(blob)
})
}
并在主代码中使用await调用它:
//* Convert resBlob to dataUrl and resolve
const resData = await blobToData(resBlob)
我发现最安全可靠的方法是使用FileReader()。
演示:映像到Base64
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
</head>
<body>
<input id="myinput" type="file" onchange="encode();" />
<div id="dummy">
</div>
<div>
<textarea style="width:100%;height:500px;" id="txt">
</textarea>
</div>
<script>
function encode() {
var selectedfile = document.getElementById("myinput").files;
if (selectedfile.length > 0) {
var imageFile = selectedfile[0];
var fileReader = new FileReader();
fileReader.onload = function(fileLoadedEvent) {
var srcData = fileLoadedEvent.target.result;
var newImage = document.createElement('img');
newImage.src = srcData;
document.getElementById("dummy").innerHTML = newImage.outerHTML;
document.getElementById("txt").value = document.getElementById("dummy").innerHTML;
}
fileReader.readAsDataURL(imageFile);
}
}
</script>
</body>
</html>
更新-相同的代码与评论@AnniekJ请求:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
</head>
<body>
<input id="myinput" type="file" onchange="encode();" />
<div id="dummy">
</div>
<div>
<textarea style="width:100%;height:500px;" id="txt">
</textarea>
</div>
<script>
function encode() {
// Get the file objects that was selected by the user from myinput - a file picker control
var selectedfile = document.getElementById("myinput").files;
// Check that the user actually selected file/s from the "file picker" control
// Note - selectedfile is an array, hence we check it`s length, when length of the array
// is bigger than 0 than it means the array containes file objects
if (selectedfile.length > 0) {
// Set the first file object inside the array to this variable
// Note: if multiple files are selected we can itterate on all of the selectedfile array using a for loop - BUT in order to not make this example complicated we only take the first file object that was selected
var imageFile = selectedfile[0];
// Set a filereader object to asynchronously read the contents of files (or raw data buffers) stored on the user's computer, using File or Blob objects to specify the file or data to read.
var fileReader = new FileReader();
// We declare an event of the fileReader class (onload event) and we register an anonimous function that will be executed when the event is raised. it is "trick" we preapare in order for the onload event to be raised after the last line of this code will be executed (fileReader.readAsDataURL(imageFile);) - please read about events in javascript if you are not familiar with "Events"
fileReader.onload = function(fileLoadedEvent) {
// AT THIS STAGE THE EVENT WAS RAISED
// Here we are getting the file contents - basiccaly the base64 mapping
var srcData = fileLoadedEvent.target.result;
// We create an image html element dinamically in order to display the image
var newImage = document.createElement('img');
// We set the source of the image we created
newImage.src = srcData;
// ANOTHER TRICK TO EXTRACT THE BASE64 STRING
// We set the outer html of the new image to the div element
document.getElementById("dummy").innerHTML = newImage.outerHTML;
// Then we take the inner html of the div and we have the base64 string
document.getElementById("txt").value = document.getElementById("dummy").innerHTML;
}
// This line will raise the fileReader.onload event - note we are passing the file object here as an argument to the function of the event
fileReader.readAsDataURL(imageFile);
}
}
</script>
</body>
</html>
以下是我所做的:
// Author James Harrington 2014
function base64(file, callback){
var coolFile = {};
function readerOnload(e){
var base64 = btoa(e.target.result);
coolFile.base64 = base64;
callback(coolFile)
};
var reader = new FileReader();
reader.onload = readerOnload;
var file = file[0].files[0];
coolFile.filetype = file.type;
coolFile.size = file.size;
coolFile.filename = file.name;
reader.readAsBinaryString(file);
}
下面是你如何使用它
base64( $('input[type="file"]'), function(data){
console.log(data.base64)
})
我最终使用了一个返回Promise的函数。
const getImg64 = async() => { const convertImgToBase64URL = (url) => { console.log(url) return new Promise((resolve, reject) => { const img = new Image(); img.crossOrigin = 'Anonymous'; img.onload = () => { let canvas = document.createElement('CANVAS') const ctx = canvas.getContext('2d') canvas.height = img.height; canvas.width = img.width; ctx.drawImage(img, 0, 0); const dataURL = canvas.toDataURL(); canvas = null; resolve(dataURL) } img.src = url; }) } //for the demonstration purposes I used proxy server to avoid cross origin error const proxyUrl = 'https://cors-anywhere.herokuapp.com/' const image = await convertImgToBase64URL(proxyUrl+'https://image.shutterstock.com/image-vector/vector-line-icon-hello-wave-260nw-1521867944.jpg') console.log(image) } getImg64()
你可以在任何异步函数中使用这种方法。然后，您只需等待转换后的图像并继续执行指示即可。
这很简单。 只需调用函数并传递你的图像。 2>保存返回值并在任何需要的地方使用。
//call like this
const convertedFile = await imageToBase64(fileObj);
console.log("convertedFile",convertedFile);
//this is the required function
async function imageToBase64(image) {
const reader = new FileReader();
reader.readAsDataURL(image);
const data= await new Promise((resolve, reject) => {
reader.onload = () => resolve(reader.result);
reader.onerror = error => reject(error);
});
return data;
}
export default imageToBase64;
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