问题描述
从 <input type="file"> 接收的文件的属性是只读的.
Properties of files received from an <input type="file"> are read-only.
例如，以下重写 file.name 的尝试要么静默失败，要么抛出 TypeError: Cannot assign to read only property 'name' of object '#<File>'.
For example, the following attempt to re-write file.name would either fail silently or throw TypeError: Cannot assign to read only property 'name' of object '#<File>'.
<input onchange="onchange" type="file">
onchange = (event) => {
const file = event.target.files[0];
file.name = 'foo';
}
尝试通过 Object.assign({}, file) 创建副本失败(创建一个空对象).
Attempting to create a copy via Object.assign({}, file) fails (creates an empty object).
那么如何克隆一个 File 对象呢?
So how does one clone a File object?
推荐答案
我的解决方案在于 File 构造函数:
My solution lay in the File constructor:
https://developer.mozilla.org/en-US/docs/Web/API/File#Implementation_notes
它本身就是Blob的扩展:
https://developer.mozilla.org/en-US/docs/Web/API/Blob/Blob
let file = event.target.files[0];
if (this.props.distro) {
const name = 'new-name-here' + // Concat with file extension.
file.name.substring(file.name.lastIndexOf('.'));
// Instantiate copy of file, giving it new name.
file = new File([file], name, { type: file.type });
}
注意 File() 的第一个参数必须是一个数组，而不仅仅是原始文件.
Note the first argument to File() must be an array, not simply the original file.
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