Angular 9异步等待未捕获(承诺中)错误

Question

//to check the uploaded pdf file total pages > 5
static validatePdfFile(event: any) {
const file = event.target.files[0];
file.arrayBuffer().then(async buff => {
let fileUint8Array = new Uint8Array(buff);
const pdfDoc = await PDFDocument.load(fileUint8Array, {updateMetadata: false});
const totalPages = pdfDoc.getPageCount();

if(totalPages > 5) {
throw new Error('File must be less than 5 pages.');
}
});
}

使用异步等待，获得以下异常：

Uncaught (in promise): Error: File must be less than 5 pages.. Error: File must be less than 5 pages. at Function. 
(http://localhost:4200/main.ca25b55f0dfc50ab2.....

从异步中抛出新错误的正确方法是什么？

Answer 1

：(

validatePdfFile(event: any) {
const file = event.target.files[0];
this.PdfPagesCount(file).subscribe(
(pageCount: number) => {
if (pageCount > 5) {
throw new Error('File must be less than 5 pages.');
} else {
//... 
}
},
(error: any) => {
event.target.value = '';
throw error;
}
);
}
countPdfPages(file: File) {
return from(file.arrayBuffer().then(
async buff => {
const fileUint8Array = new Uint8Array(buff);
const pdfDoc = await PDFDocument.load(fileUint8Array, {updateMetadata: false, ignoreEncryption: true});
return pdfDoc.getPageCount();
}
));
}