我怎么能转换成一个onload事件的诺言成异步/等待 [英] How can I convert an onload promise into Async/Await

问题描述

我有以下的打字稿，我想用异步 / 等待上。但我似乎无法在我的头上理清如何做到这一点。

 私人getWorkbookFromFile2（excelFile：文件）：无极＆LT; xlsx.IWorkBook＆GT; {
    VAR loadedPromise =新承诺＆LT; xlsx.IWorkBook＆GT;（（解决，拒绝）=＆GT; {
        VAR读卡器=新的FileReader（）;        reader.onload =（事件：任意）=＆GT; {
            VAR数据= event.target.result;            VAR工作簿= xlsx.read（数据，{类型：'二进制'}）;            的console.log（workbook.SheetNames）;
            解决（练习册）;
        };
        reader.readAsBinaryString（excelFile）;
    }）;    返回loadedPromise;
}
 

有人能告诉我这个打字稿承诺如何转化为使用异步 / 等待

解决方案

  

打字稿现在支持异步功能引擎，具有ES6发电机，例如原生支持节点v4和上方。异步功能与async关键字pfixed $ P $;等待暂停执行，直到一个异步函数返回的承诺得到满足，并解开自许返回的值。 - 来源

 异步函数getWorkbookFromFile2（excelFile：文件）{
    返回新承诺＆LT; xlsx.IWorkBook＆GT;（（解决，拒绝）=＆GT; {
        VAR读卡器=新的FileReader（）;        reader.onload =（事件：任意）=＆GT; {
            VAR数据= event.target.result;            VAR工作簿= xlsx.read（数据，{类型：'二进制'}）;            的console.log（workbook.SheetNames）;
            解决（练习册）;
        };
        reader.readAsBinaryString（excelFile）;
    }）;
}
 

例如功耗：

 异步调用函数（）{
    变种簿=等待this.getWorkbookFromFile2（this.getFile（））;
    //在工作簿变量是一个IWorkBook ...
}
 

I have the following Typescript that I would like to use async/await on. But I can't seem to sort it out in my head how to do this.

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

解决方案

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

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:

async function caller() {
    var workbook = await this.getWorkbookFromFile2(this.getFile());
    // The 'workbook' variable is an IWorkBook...
}

这篇关于我怎么能转换成一个onload事件的诺言成异步/等待的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！