Javascript Node.js可以';不履行承诺(承诺{<;待定>;})
我是异步编码新手 我正在使用csvtojson库,试图转换一个csv文件并将结果传递到另一个模块 convert()函数如下所示:Javascript Node.js可以';不履行承诺(承诺{<;待定>;}),javascript,node.js,es6-promise,Javascript,Node.js,Es6 Promise,我是异步编码新手 我正在使用csvtojson库,试图转换一个csv文件并将结果传递到另一个模块 convert()函数如下所示: convert: function (csvFilePath) { return new Promise((resolve, reject) => { const options = { delimiter: ["|",","], noHeader: true ,
convert: function (csvFilePath) {
return new Promise((resolve, reject) => {
const options = { delimiter: ["|",","],
noHeader: true ,
headers: ["header1", "header2"]
}
csv(options)
.fromFile(csvFilePath)
.on('end_parsed',(convertedJson) => {
resolve(convertedJson);
})
.on("done",(error) => {
reject(error);
})
});
}
我的电话:
const converter = require ("./converter")();
let json;
json = converter.convert("./importSample.csv");
console.log(json);
当我执行代码时,我可以看到承诺仍然处于挂起状态:
Promise{}
我想我必须使用
.then()
函数,但我不知道在哪里或如何使用。从转换器
函数中,您得到了承诺,并且该对象具有方法then
。你应该这样做
const converter = require ("./converter")();
converter.convert("./importSample.csv").then(json => {
console.log(json);
}).catch(error => {
console.log(error);
});
你可以找到很好的关于承诺的教程,这是承诺的文档。从
转换器
函数中,你可以得到承诺,并且该对象有方法,然后
。你应该这样做
const converter = require ("./converter")();
converter.convert("./importSample.csv").then(json => {
console.log(json);
}).catch(error => {
console.log(error);
});
您可以找到关于承诺的不错的教程,这是承诺的文档。承诺有一个固定的语法体系结构。我将用一个简单的代码来解释它
var x = new Promise((resolve,reject)=>{
//here you perform an asynchronous call
resolve(value); //receive it in 'then' part of promise
reject(error): //if your operation fails due to any error, you call reject, which is handled by 'catch' part of the promise.
});
x.then((value)=>{
//this is the part which was called using resolve, and the value it receives is the value you passed as argument in resolve.
});
x.catch((error)=>{
//this part is called by reject. the error received is the value you passed inside the reject.
});
因此,您的函数应该类似于-
converter.convert("./importSample.csv").then((json)=>{
//here is your part of code which is to be handled synchronously after the promise is called.
}).catch((error)=>{
//in case any error occurs and you want your program to exit gracefully.
});
Promise有一个固定的语法结构。我将用一个简单的代码来解释它
var x = new Promise((resolve,reject)=>{
//here you perform an asynchronous call
resolve(value); //receive it in 'then' part of promise
reject(error): //if your operation fails due to any error, you call reject, which is handled by 'catch' part of the promise.
});
x.then((value)=>{
//this is the part which was called using resolve, and the value it receives is the value you passed as argument in resolve.
});
x.catch((error)=>{
//this part is called by reject. the error received is the value you passed inside the reject.
});
因此,您的函数应该类似于-
converter.convert("./importSample.csv").then((json)=>{
//here is your part of code which is to be handled synchronously after the promise is called.
}).catch((error)=>{
//in case any error occurs and you want your program to exit gracefully.
});