UPD TypeScript版本也可在答案
现在我通过这一行获取File object:
file = document.querySelector('#files > input[type="file"]').files[0]
我需要通过json在基数64发送这个文件。我应该怎么做才能将其转换为base64字符串?
UPD TypeScript版本也可在答案
现在我通过这一行获取File object:
file = document.querySelector('#files > input[type="file"]').files[0]
我需要通过json在基数64发送这个文件。我应该怎么做才能将其转换为base64字符串?
当前回答
如果你在寻找一个基于承诺的解决方案,这是@Dmitri的代码适应:
function getBase64(file) {
return new Promise((resolve, reject) => {
const reader = new FileReader();
reader.readAsDataURL(file);
reader.onload = () => resolve(reader.result);
reader.onerror = error => reject(error);
});
}
var file = document.querySelector('#files > input[type="file"]').files[0];
getBase64(file).then(
data => console.log(data)
);
其他回答
这是
// fileObj: File
const base64 = window.URL.createObjectURL(fileObj);
// You can use it with <img src={base64} />
JavaScript btoa()函数可用于将数据转换为base64编码的字符串
<div>
<div>
<label for="filePicker">Choose or drag a file:</label><br>
<input type="file" id="filePicker">
</div>
<br>
<div>
<h1>Base64 encoded version</h1>
<textarea id="base64textarea"
placeholder="Base64 will appear here"
cols="50" rows="15"></textarea>
</div>
</div>
var handleFileSelect = function(evt) {
var files = evt.target.files;
var file = files[0];
if (files && file) {
var reader = new FileReader();
reader.onload = function(readerEvt) {
var binaryString = readerEvt.target.result;
document.getElementById("base64textarea").value = btoa(binaryString);
};
reader.readAsBinaryString(file);
}
};
if (window.File && window.FileReader && window.FileList && window.Blob) {
document.getElementById('filePicker')
.addEventListener('change', handleFileSelect, false);
} else {
alert('The File APIs are not fully supported in this browser.');
}
现代ES6路(异步/await)
const toBase64 = file => new Promise((resolve, reject) => {
const reader = new FileReader();
reader.readAsDataURL(file);
reader.onload = () => resolve(reader.result);
reader.onerror = error => reject(error);
});
async function Main() {
const file = document.querySelector('#myfile').files[0];
console.log(await toBase64(file));
}
Main();
UPD:
如果你想捕捉错误
async function Main() {
const file = document.querySelector('#myfile').files[0];
try {
const result = await toBase64(file);
return result
} catch(error) {
console.error(error);
return;
}
//...
}
下面是我写的几个函数,用于获得json格式的文件,可以轻松传递:
//takes an array of JavaScript File objects
function getFiles(files) {
return Promise.all(files.map(getFile));
}
//take a single JavaScript File object
function getFile(file) {
const reader = new FileReader();
return new Promise((resolve, reject) => {
reader.onerror = () => { reader.abort(); reject(new Error("Error parsing file"));}
reader.onload = function () {
//This will result in an array that will be recognized by C#.NET WebApi as a byte[]
let bytes = Array.from(new Uint8Array(this.result));
//if you want the base64encoded file you would use the below line:
let base64StringFile = btoa(bytes.map((item) => String.fromCharCode(item)).join(""));
//Resolve the promise with your custom file structure
resolve({
bytes,
base64StringFile,
fileName: file.name,
fileType: file.type
});
}
reader.readAsArrayBuffer(file);
});
}
//using the functions with your file:
file = document.querySelector('#files > input[type="file"]').files[0]
getFile(file).then((customJsonFile) => {
//customJsonFile is your newly constructed file.
console.log(customJsonFile);
});
//if you are in an environment where async/await is supported
files = document.querySelector('#files > input[type="file"]').files
let customJsonFiles = await getFiles(files);
//customJsonFiles is an array of your custom files
console.log(customJsonFiles);
打印稿版本
const file2Base64 = (file:File):Promise<string> => {
return new Promise<string> ((resolve,reject)=> {
const reader = new FileReader();
reader.readAsDataURL(file);
reader.onload = () => resolve(reader.result?.toString() || '');
reader.onerror = error => reject(error);
})
}