typescript 输入'字符串| ArrayBuffer' 不可分配给类型 'string'
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/52955710/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Type 'string | ArrayBuffer' is not assignable to type 'string'
提问by Aragorn
TypeScript error for reading string from FileReader
从 FileReader 读取字符串的 TypeScript 错误
Simple code to read file contents:
读取文件内容的简单代码：
const reader: FileReader = new FileReader();
reader.readAsText(file);
reader.onload = (e) => {
const csv: string = reader.result; -> getting TS error on this line
}
TypeScript error I get:
我得到的打字稿错误：
Type 'string | ArrayBuffer' is not assignable to type 'string'.
Type 'ArrayBuffer' is not assignable to type 'string'.
回答by Nurbol Alpysbayev
The error message says it all.
错误消息说明了一切。
You declare a stringtype of csvvariable.
You then assign string | ArrayBuffertype (of reader.result) to the stringtype, you just assigned. You cannot. You only can assign stringto string.
您声明了一种string类型的csv变量。然后将string | ArrayBuffertype (of reader.result)分配给string刚刚分配的类型。你不能。您只能分配string给string.
So, if you 100% sure that reader.resultcontains stringyou could assert this:
因此，如果您 100% 确定reader.result包含string您可以断言：
const csv: string = reader.result as string;
However if you are not sure, do this:
但是，如果您不确定，请执行以下操作：
const csv: string | ArrayBuffer = reader.result;
// or simply:
const csv = reader.result; // `string | ArrayBuffer` type is inferred for you
Then you typically should have some check like:
那么您通常应该进行一些检查，例如：
if (typeof csv === 'string') {/*use csv*/}
else {/* use csv.toString() */}
回答by villy393
This will always output a string regardless if csvis a stringor an ArrayBuffer.
这将始终输出一个字符串，无论csv是 astring还是 an ArrayBuffer。
const csv: string = typeof csv === 'string' ? csv : Buffer.from(csv).toString()
