如何在 JavaScript 中创建文件对象的修改副本?

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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