I'm trying to remove the then statements from the following piece of code and then replace all the catches with try/catch statements. I'm having some issues knowing what to do with the then statements.
export class WelcomePageContribution implements IWorkbenchContribution {
constructor(
#IInstantiationService instantiationService: IInstantiationService,
#IConfigurationService configurationService: IConfigurationService,
#IEditorService editorService: IEditorService,
#IBackupFileService backupFileService: IBackupFileService,
#IFileService fileService: IFileService,
#IWorkspaceContextService contextService: IWorkspaceContextService,
#ILifecycleService lifecycleService: ILifecycleService,
#ICommandService private readonly commandService: ICommandService,
) {
const enabled = isWelcomePageEnabled(configurationService, contextService);
if (enabled && lifecycleService.startupKind !== StartupKind.ReloadedWindow) {
backupFileService.hasBackups().then(hasBackups => {
const activeEditor = editorService.activeEditor;
if (!activeEditor && !hasBackups) {
const openWithReadme = configurationService.getValue(configurationKey) === 'readme';
if (openWithReadme) {
return Promise.all(contextService.getWorkspace().folders.map(folder => {
const folderUri = folder.uri;
return fileService.resolve(folderUri)
.then(folder => {
const files = folder.children ? folder.children.map(child => child.name) : [];
const file = arrays.find(files.sort(), file => strings.startsWith(file.toLowerCase(), 'readme'));
if (file) {
return joinPath(folderUri, file);
}
return undefined;
}, onUnexpectedError);
})).then(arrays.coalesce)
.then<any>(readmes => {
if (!editorService.activeEditor) {
if (readmes.length) {
const isMarkDown = (readme: URI) => strings.endsWith(readme.path.toLowerCase(), '.md');
return Promise.all([
this.commandService.executeCommand('markdown.showPreview', null, readmes.filter(isMarkDown), { locked: true }),
editorService.openEditors(readmes.filter(readme => !isMarkDown(readme))
.map(readme => ({ resource: readme }))),
]);
} else {
return instantiationService.createInstance(WelcomePage).openEditor();
}
}
return undefined;
});
} else {
return instantiationService.createInstance(WelcomePage).openEditor();
}
}
return undefined;
}).then(undefined, onUnexpectedError);
}
}
}
so that the entire thing reads more like this..
const enabled = await isWelcomePageEnabled(configurationService, contextService);
if (enabled && lifecycleService.startupKind !== StartupKind.ReloadedWindow) {
const hasBackups = await backupFileService.hasBackups();
const activeEditor = editorService.activeEditor;
if (!activeEditor && !hasBackups) {
const openWithReadme = configurationService.getValue(configurationKey) === 'readme';
if (openWithReadme) {
...
It looks like you're on the right track with your second code block. then is called on a promise, so instead of using then you would await the function then was called on, save it to a variable, and then move the code that was in the callback to then below the await at the same indentation level. Whenever you await, you can wrap it in a try/catch and put what would have been in the catch callback inside of the catch block.
So for example
fetchData().then(data => {
console.log(data)
}).catch(err => {
console.error(err)
})
becomes
try {
const data = await fetchData()
console.log(data)
}
catch (err) {
console.error(err)
}
The complication in your example is that the code is in a class constructor, and those can't be async.
Related
I am using the google translate api to translate data from a json file to french locale and then write it back to a file. I am using a recursive function to iterate over the json file since it is deeply nested. However the execution is not waiting till the translation is completed before it writes to the file. I have tried using callback and promise approaches but i couldn't get it right.
Just for it to work as I required an output as an emergency I have set a timout before the write method is called. It work but I would like to learn the appropriate/correct approach to implement this.
const fs = require('fs')
const {Translate} = require('#google-cloud/translate').v2
require('dotenv').config()
process.env['NODE_TLS_REJECT_UNAUTHORIZED'] = 0
const credentials = JSON.parse(process.env.credentials)
const translate = new Translate({
credentials,
projectId: credentials.project_id,
})
let data = {}
// writeJSONTofile should be executed only after readJSONFile execution is completed
//read file
const readJSONFile = () => {
try {
data = JSON.parse(fs.readFileSync('...\\locale\\en.json'))
iterateAndTranslate(data)
setTimeout(() => {
writeJSONToFile()
}, 25000)
} catch (error) {
console.log(error)
}
}
// iterate, translate, reassign
const iterateAndTranslate = async (data) => {
for(key in data) {
if (typeof data[key] === 'object' && data[key] !== null) {
iterateAndTranslate(data[key])
} else{
data[key] = await translateText(data[key], 'fr')
}
}
}
//translate method
const translateText = async (text, targetLanguage) => {
try {
let [response] = await translate.translate(text, targetLanguage)
return response
} catch (error) {
console.log(error)
return 0
}
}
const writeJSONToFile = async () => {
var outputFileName = 'C:\\test\\test.json'
await fs.writeFileSync(outputFileName, JSON.stringify(data,null,4), (err) => {
if(err) {
console.log(err)
} else {
console.log('Done!')
}
})
}
// start from here
readJSONFile()
You have a few issues with your code.
Your functions use a global variable and mutate it instead of getting input and returning output.
timeout will cause unexpected behavior in your case.
you are using var
you have redundant async-await on the writeJSONToFile function
See my view of point about the possible solution.
const fs = require("fs");
const { Translate } = require("#google-cloud/translate").v2;
require("dotenv").config();
process.env["NODE_TLS_REJECT_UNAUTHORIZED"] = 0;
const credentials = JSON.parse(process.env.credentials);
const translate = new Translate({
credentials,
projectId: credentials.project_id,
});
// writeJSONTofile should be executed only after readJSONFile execution is completed
//read file
const readJSONFile = async () => {
try {
const data = JSON.parse(fs.readFileSync("...\\locale\\en.json"));
return iterateAndTranslate(data);
} catch (error) {
console.log(error);
}
return {};
};
// iterate, translate, reassign
const iterateAndTranslate = async (data) => {
for (let key in data) {
if (typeof data[key] === "object" && data[key] !== null) {
await iterateAndTranslate(data[key]);
} else {
data[key] = await translateText(data[key], "fr");
}
}
return data;
};
//translate method
const translateText = async (text, targetLanguage) => {
try {
let [response] = await translate.translate(text, targetLanguage);
return response;
} catch (error) {
console.log(error);
}
return null;
};
const writeJSONToFile = (data) => {
let outputFileName = "C:\\test\\test.json";
fs.writeFileSync(outputFileName, JSON.stringify(data, null, 4), (err) => {
if (err) {
console.log(err);
} else {
console.log("Done!");
}
});
};
// start from here
const run = async () => {
const data = await readJSONFile();
writeJSONToFile(data);
};
run();
See more:
why not using global varible
why not using var
First of all I am a newbie in nodejs, please be indulgent :)
I have a problem with some async functions. In my case, a first API call is made and then a sub call is made on every item returned. this is my code after the first call is made :
const countryStatesCalls: Promise<any>[] = [];
countries.forEach((country, index) => {
countries[index] = convertToCountry(country);
const countryStatesCall = (countryId: number) => {
return new Promise((resolve, reject) => {
const countryStatesList = getStateCountries(countryId);
if (countryStatesList) {
if (Object.prototype.toString.call(countryStatesList) !== '[object Array]') {
resolve([]);
} else {
resolve(countryStatesList);
}
} else {
reject([]);
}
});
};
countryStatesCalls.push(
countryStatesCall(countries[index].id).then(countryStates => {
countries[index].states = countryStates;
}).catch(countryStatesType => {
countries[index].states = countryStatesType;
})
);
});
await Promise.all(countryStatesCalls).then(_ => {
res.json(countries)
});
the following code
res.json(countries)
is supposed to be executed after all promises execution has been finished.
EDIT : the getStateCountries async function :
const getStateCountries = async (countryId: number, lang?: string) => {
const listState = await odoo.searchRead(
'res.country.state',
{
filters: [
{
field: 'country_id',
operator: '=',
value: countryId,
},
],
fields: fieldState,
},
{ lang }
);
if (!listState.length) {
return [];
} else {
listState.forEach((state, index) => {
listState[index] = convertToState(state);
});
return listState;
}
};
the main function is an express controller
I think my mistake may be obvious but can you help me please, I read many topics and I cannot see what am I doing wrong.
Thank you in advance
[SOLUTION]
As pointed out by comments, I was doing it the wrong way around, my call on promise called another promise: the solution was to write :
const countryStatesCalls: Promise<any>[] = [];
for (let index = 0; index < countries.length; index++) {
countries[index] = convertToCountry(countries[index]);
if (withSates) {
countryStatesCalls.push(
getStateCountries(countries[index].id)
);
} else {
countries[index].states = [];
}
}
if (withSates) {
await Promise.all(countryStatesCalls).then((countriesStates) => {
countries.forEach((country, index) => {
country.states = [];
for (const countryStates of countriesStates) {
if (countryStates.length
&& countryStates[0].country_id.code === country.id) {
countries[index].states = countryStates;
}
}
});
res.json(countries);
});
} else {
res.json(countries);
}
thank you everyone
I can't exactly tell why it doesn't work, but this looks a bit like the Promise constructor antipattern. The getStateCountries function is async and already creates a promise, so you need to await it or chain .then() to it. The new Promise is not necessary.
Also I'd recommend to avoid forEach+push, rather just use map, and get rid of the countryStatesCall helper:
const countryStatesCalls: Promise<any>[] = countries.map((country, index) => {
countries[index] = convertToCountry(country);
return getStateCountries(countries[index].id).then(countryStatesList => {
if (countryStatesList) {
if (Object.prototype.toString.call(countryStatesList) !== '[object Array]') {
return [];
} else {
return countryStatesList;
}
} else {
throw new Error("getStateCountries() resolved to nothing");
}
}).then(countryStates => {
countries[index].states = countryStates;
});
});
await Promise.all(countryStatesCalls).then(_ => {
res.json(countries)
});
I am sure this is something basic that I am missing but it's late and my brain gets like that. So I have this function:
export const createRandomHex = () => {
try {
return crypto.randomBytes(127, (_err, buf) => {
console.log("[create] bearerToken: ", buf.toString("hex"));
const bearerTokenString = buf.toString("hex");
return bearerTokenString;
});
} catch (e) {
return e;
}
};
And I am calling it in another function as such:
export const createBearerToken = () => {
const bearerToken = createRandomHex();
}
For some reason, the value of bearerToken in the createBearerToken is undefined or null. Can anyone help me with this?
randomBytes is asynchronous and takes a callback. You could return a promise in your function:
export const createRandomHex = async () => {
return new Promise((resolve, reject) => {
try {
return crypto.randomBytes(127, (_err, buf) => {
console.log("[create] bearerToken: ", buf.toString("hex"));
const bearerTokenString = buf.toString("hex");
resolve(bearerTokenString);
});
} catch (e) {
reject(e);
}
});
};
I'm exporting/importing an empty array to implement MVC patern and I was able to successfully store data in it by calling the allMentors method on the Mentor class.
Secondly, I want to be DRY and get the data from the array and then use it to find a specific mentor but I'm getting an empty array.
I searched the internet and I followed the example of using this keyword and call the static method inside another but NodeJS is throwing an error that this is undefined.
ALL MENTORS method
class Mentor{
static async allMentors(req, res) {
try {
users.forEach(user => {
if(user.is_mentor === true) {
mentors.push(user);
}
})
const ObjKeyRename = (src, map) => {
const dst = {};
for (const key in src) {
if (key in map)
// rename key
dst[map[key]] = src[key];
else
// same key
dst[key] = src[key];
}
return dst;
};
const uniqueMentors = Array.from(new Set(mentors.map(m => m.id)))
.map(id => {
return new Promise((resolve, reject)=> {
const currMentor = mentors.find(m => m.id === id);
const modMentor = ObjKeyRename(currMentor, { "id": "mentorId" });
return resolve(modMentor);
})
})
Promise.all(uniqueMentors).then(output => {
output.forEach(async obj => {
await delete obj['password'];
})
return res
.status(200)
.json(new ResponseHandler(200, 'All Mentors', output, null).result());
})
} catch (err) {
return res
.status(500)
.json(new ResponseHandler(500, err.message, null).result());
}
}
static async singleMentor(req, res) {
const returnedMentors = this.allMentors;
console.log('THE RETURNED:',returnedMentors)
const theMentor = returnedMentors.find(u => u.mentorId === parseInt(req.params.mentorId));
try {
if (!theMentor) return res
.status(404)
.json(new ResponseHandler(404, `Mentor number ${req.params.mentorId} not found`, null).result());
return res
.status(200)
.json(new ResponseHandler(200, 'Your mentor', theMentor, null).result());
} catch (err) {
return res
.status(500)
.json(new ResponseHandler(500, err.message, null).result())
}
}
}
export default Mentor;
What am I doing wrong? I appreciate your continued help as a JS learner.
There are multiple problems with your code:
a static method needs to be called by Class (Mentor) not by Reference (this)
a async method needs to be awaited or called with a callback (.then())
So for example you have the class MentorHandler:
class Mentor {
constructor() {
}
static async singleMentor(req, res) {
// ... some more code
}
static async allMentors(req, res) {
// await the result of the method
// call by class
const returnedMentors = await Mentor.allMentors();
// ... some more code
}
}
I made a Storage.js file with some Utils function. In most case, I use it in this way:
async someFunction()=>{ let foo = await getOnDevice(someName)}
But the in my case, I have a problem with the syntax
import {AsyncStorage} from 'react-native'
export const saveOnDevice = async (name, data) => {
try {
if (data !== null && data !== undefined) {
await AsyncStorage.setItem(name, JSON.stringify(data));
}
} catch (error) {
console.log(error)
}
};
export const getOnDevice = async (name) => {
try {
const data = await AsyncStorage.getItem(name);
if (data !== null && data !== undefined) {
return data
}
} catch (error) {
console.log(error)
}
};
How can I use it without declaring an async function?
import {saveOnDevice} from '../../utils/Storage'
export function fetchUrlWithRedux(url) {
return (dispatch) => {
dispatch(fetchUrlRequest(url));
return fetchUrl(url, dispatch).then(([response, json]) => {
if (response.status === 200) {
saveOnDevice('url', json.data.host);
dispatch(fetchUrlSuccess(json))
}
else {
dispatch(fetchUrlError())
}
}).catch(() => dispatch(fetchUrlError()))
}
}
What is wrong with my code?
If you don't want to use async/await in your main file then you can use promise, like below.
saveOnDevice('url', json.data.host).then(() => {
dispatch(fetchUrlSuccess(json))
})
I think you need to add async before the anonymous function passed to .then(), and await before the call to saveOnDevice():
import {saveOnDevice} from '../../utils/Storage'
export function fetchUrlWithRedux(url) {
return (dispatch) => {
dispatch(fetchUrlRequest(url));
return fetchUrl(url, dispatch).then(async ([response, json]) => {
if (response.status === 200) {
await saveOnDevice('url', json.data.host);
dispatch(fetchUrlSuccess(json))
}
else {
dispatch(fetchUrlError())
}
}).catch(() => dispatch(fetchUrlError()))
}
}