typescript 如何将 onload 承诺转换为 Async/Await
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How can I convert an onload promise into Async/Await
提问by Vaccano
I have the following Typescript that I would like to use async/awaiton. But I can't seem to sort it out in my head how to do this.
我有以下我想在async/await上使用的打字稿。但我似乎无法在脑海中弄清楚如何做到这一点。
private getWorkbookFromFile2(excelFile: File): Promise<xlsx.IWorkBook> {
var loadedPromise = new Promise<xlsx.IWorkBook>((resolve, reject) => {
var reader = new FileReader();
reader.onload = (event: any) => {
var data = event.target.result;
var workbook = xlsx.read(data, { type: 'binary' });
console.log(workbook.SheetNames);
resolve(workbook);
};
reader.readAsBinaryString(excelFile);
});
return loadedPromise;
}
Can someone show me how this Typescript promise can be converted to use async/await
有人可以告诉我如何将此 Typescript 承诺转换为使用async/await
回答by David Pine
TypeScript now supports asynchronous functions for engines that have native support for ES6 generators, e.g. Node v4 and above. Asynchronous functions are prefixed with the async keyword; await suspends the execution until an asynchronous function return promise is fulfilled and unwraps the value from the Promise returned. - Source
TypeScript 现在支持对 ES6 生成器具有本机支持的引擎的异步函数，例如 Node v4 及更高版本。异步函数以 async 关键字为前缀；await 挂起执行，直到异步函数返回承诺完成并从返回的承诺中解包值。-来源
async function getWorkbookFromFile2(excelFile: File) {
return new Promise<xlsx.IWorkBook>((resolve, reject) => {
var reader = new FileReader();
reader.onload = (event: any) => {
var data = event.target.result;
var workbook = xlsx.read(data, { type: 'binary' });
console.log(workbook.SheetNames);
resolve(workbook);
};
reader.readAsBinaryString(excelFile);
});
}
Example consumption:
消费举例：
async function caller() {
var workbook = await this.getWorkbookFromFile2(this.getFile());
// The 'workbook' variable is an IWorkBook...
}
