Mixing
Promises with NodeJS
I'd like to use promises with NodeJS but it seems not working as expected.
I'd like to see LOG 1, LOG 2 and LOG 3 for all files in this order. And LOG 4 is hidden...
But I get this :
LOG 1
LOG 3
LOG 1
LOG 3
LOG 1
LOG 3
SUCCESS LOG 2
SUCCESS LOG 2
SUCCESS LOG 2
SUCCESS LOG 2
My code :
var filePromise = _.map(files, function(file) {
var filePath = './sql/' + file;
fs.lstat(filePath, function(err, stats) {
if (stats.isFile() && file !== '.gitignore' && file !== 'index.js') {
fs.readFile(filePath, 'utf-8', function(err, data) {
console.log('LOG 1');
db.query(data).then(function() {
console.log(colors.green('SUCCESS LOG 2'));
}).catch(function() {
console.log(colors.red('ERROR LOG 2'));
});
console.log('LOG 3');
});
}
});
});
Promise.all(filePromise).then(function() {
console.log(colors.green('LOG 4'));
});
node.js promise
asked Nov 22 '18 at 13:37
tonymx227tonymx227
1,676113161
add a comment |
I'd like to use promises with NodeJS but it seems not working as expected.
I'd like to see LOG 1, LOG 2 and LOG 3 for all files in this order. And LOG 4 is hidden...
But I get this :
LOG 1
LOG 3
LOG 1
LOG 3
LOG 1
LOG 3
SUCCESS LOG 2
SUCCESS LOG 2
SUCCESS LOG 2
SUCCESS LOG 2
My code :
var filePromise = _.map(files, function(file) {
var filePath = './sql/' + file;
fs.lstat(filePath, function(err, stats) {
if (stats.isFile() && file !== '.gitignore' && file !== 'index.js') {
fs.readFile(filePath, 'utf-8', function(err, data) {
console.log('LOG 1');
db.query(data).then(function() {
console.log(colors.green('SUCCESS LOG 2'));
}).catch(function() {
console.log(colors.red('ERROR LOG 2'));
});
console.log('LOG 3');
});
}
});
});
Promise.all(filePromise).then(function() {
console.log(colors.green('LOG 4'));
});
node.js promise
asked Nov 22 '18 at 13:37
tonymx227tonymx227
1,676113161
1
Your database query us async call. It will skip that block and begins next execution. You can use async/await or place your code inside of the then block of the query
– Sagar
Nov 22 '18 at 13:43
As @Sagar said, the execution does not pause at thedb.queryasync call. Instead once the async action has been triggered, the main thread will jump to the next line and continue execution.
– Luke Stoward
Nov 22 '18 at 14:41
add a comment |
I'd like to use promises with NodeJS but it seems not working as expected.
I'd like to see LOG 1, LOG 2 and LOG 3 for all files in this order. And LOG 4 is hidden...
But I get this :
LOG 1
LOG 3
LOG 1
LOG 3
LOG 1
LOG 3
SUCCESS LOG 2
SUCCESS LOG 2
SUCCESS LOG 2
SUCCESS LOG 2
My code :
var filePromise = _.map(files, function(file) {
var filePath = './sql/' + file;
fs.lstat(filePath, function(err, stats) {
if (stats.isFile() && file !== '.gitignore' && file !== 'index.js') {
fs.readFile(filePath, 'utf-8', function(err, data) {
console.log('LOG 1');
db.query(data).then(function() {
console.log(colors.green('SUCCESS LOG 2'));
}).catch(function() {
console.log(colors.red('ERROR LOG 2'));
});
console.log('LOG 3');
});
}
});
});
Promise.all(filePromise).then(function() {
console.log(colors.green('LOG 4'));
});
node.js promise
asked Nov 22 '18 at 13:37
tonymx227tonymx227
1,676113161
I'd like to use promises with NodeJS but it seems not working as expected.
I'd like to see LOG 1, LOG 2 and LOG 3 for all files in this order. And LOG 4 is hidden...
But I get this :
LOG 1
LOG 3
LOG 1
LOG 3
LOG 1
LOG 3
SUCCESS LOG 2
SUCCESS LOG 2
SUCCESS LOG 2
SUCCESS LOG 2
My code :
var filePromise = _.map(files, function(file) {
var filePath = './sql/' + file;
fs.lstat(filePath, function(err, stats) {
if (stats.isFile() && file !== '.gitignore' && file !== 'index.js') {
fs.readFile(filePath, 'utf-8', function(err, data) {
console.log('LOG 1');
db.query(data).then(function() {
console.log(colors.green('SUCCESS LOG 2'));
}).catch(function() {
console.log(colors.red('ERROR LOG 2'));
});
console.log('LOG 3');
});
}
});
});
Promise.all(filePromise).then(function() {
console.log(colors.green('LOG 4'));
});
node.js promise
node.js promise
asked Nov 22 '18 at 13:37
tonymx227tonymx227
1,676113161
asked Nov 22 '18 at 13:37
tonymx227tonymx227
1,676113161
asked Nov 22 '18 at 13:37
tonymx227tonymx227
1,676113161
asked Nov 22 '18 at 13:37
tonymx227tonymx227
1,676113161
asked Nov 22 '18 at 13:37
tonymx227tonymx227
1,676113161
1,676113161
1
Your database query us async call. It will skip that block and begins next execution. You can use async/await or place your code inside of the then block of the query
– Sagar
Nov 22 '18 at 13:43
As @Sagar said, the execution does not pause at thedb.queryasync call. Instead once the async action has been triggered, the main thread will jump to the next line and continue execution.
– Luke Stoward
Nov 22 '18 at 14:41
add a comment |
1
Your database query us async call. It will skip that block and begins next execution. You can use async/await or place your code inside of the then block of the query
– Sagar
Nov 22 '18 at 13:43
As @Sagar said, the execution does not pause at thedb.queryasync call. Instead once the async action has been triggered, the main thread will jump to the next line and continue execution.
– Luke Stoward
Nov 22 '18 at 14:41
1
1
Your database query us async call. It will skip that block and begins next execution. You can use async/await or place your code inside of the then block of the query
– Sagar
Nov 22 '18 at 13:43
Your database query us async call. It will skip that block and begins next execution. You can use async/await or place your code inside of the then block of the query
– Sagar
Nov 22 '18 at 13:43
As @Sagar said, the execution does not pause at the
db.query async call. Instead once the async action has been triggered, the main thread will jump to the next line and continue execution.– Luke Stoward
Nov 22 '18 at 14:41
As @Sagar said, the execution does not pause at the
db.query async call. Instead once the async action has been triggered, the main thread will jump to the next line and continue execution.– Luke Stoward
Nov 22 '18 at 14:41
add a comment |
1 Answer
1
active
oldest
votes
In order for filePromise to contain a collection of promises, you need to return a promise for each iteration of your map call. Only then will the call to Promise.all be evaluated correctly.
var filePromise = _.map(files, function(file) {
return new Promise(function(resolve, reject) {
var filePath = './sql/' + file;
fs.lstat(filePath, function(err, stats) {
if (stats.isFile() && file !== '.gitignore' && file !== 'index.js') {
fs.readFile(filePath, 'utf-8', function(err, data) {
console.log('LOG 1');
db.query(data).then(function() {
console.log(colors.green('SUCCESS LOG 2'));
resolve();
}).catch(function() {
console.log(colors.red('ERROR LOG 2'));
reject();
});
console.log('LOG 3');
});
} else {
reject(new Error("failed condition"))
}
});
})
});
Promise.all(filePromise).then(function() {
console.log(colors.green('LOG 4'));
});
This does not fix the ordering of your console logs. That is a separate issue. Your console logs are not actually out of order, they are logging as expected. However, this is due to the async call you are making to db.query which, when triggered does not block waiting for a response. Instead the next line is executed immediately after the function call returns.
Side note: Make sure to handle your err arguments passed to the inline callback functions of fs.lstat and fs.readFile. Failure to do so will result in the promise never completing in the event of an error.
answered Nov 22 '18 at 14:51
Luke StowardLuke Stoward
636917
Thank you. :) It works !
– tonymx227
Nov 23 '18 at 12:47
@tonymx227 not sure I'd be swallowing the internal errors as displayed here (and in your original code), the errors should be propagated up the stack and handled elsewhere or at least be logged better inline.
– James
Nov 23 '18 at 15:46
@James I did state that in the "Side note" below the code.
– Luke Stoward
Nov 26 '18 at 16:04
@LukeStoward you did, but as a bare minimum to ensure your code works e.g. your code doesn't propagate the error fromdb.queryso if that fails, the callstack is lost. Just emphasising the point to the OP that swallowing errors, in general, usually isn't a good idea.
– James
Nov 26 '18 at 16:17
@James Agree completely. I (perhaps wrongly) left the error handling logic out, since the example was already quite big. Hopefully, the OP read all of the solution and is handling errors.
– Luke Stoward
Nov 26 '18 at 16:50
add a comment |
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1 Answer
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1 Answer
1
active
oldest
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oldest
votes
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oldest
votes
In order for filePromise to contain a collection of promises, you need to return a promise for each iteration of your map call. Only then will the call to Promise.all be evaluated correctly.
var filePromise = _.map(files, function(file) {
return new Promise(function(resolve, reject) {
var filePath = './sql/' + file;
fs.lstat(filePath, function(err, stats) {
if (stats.isFile() && file !== '.gitignore' && file !== 'index.js') {
fs.readFile(filePath, 'utf-8', function(err, data) {
console.log('LOG 1');
db.query(data).then(function() {
console.log(colors.green('SUCCESS LOG 2'));
resolve();
}).catch(function() {
console.log(colors.red('ERROR LOG 2'));
reject();
});
console.log('LOG 3');
});
} else {
reject(new Error("failed condition"))
}
});
})
});
Promise.all(filePromise).then(function() {
console.log(colors.green('LOG 4'));
});
This does not fix the ordering of your console logs. That is a separate issue. Your console logs are not actually out of order, they are logging as expected. However, this is due to the async call you are making to db.query which, when triggered does not block waiting for a response. Instead the next line is executed immediately after the function call returns.
Side note: Make sure to handle your err arguments passed to the inline callback functions of fs.lstat and fs.readFile. Failure to do so will result in the promise never completing in the event of an error.
answered Nov 22 '18 at 14:51
Luke StowardLuke Stoward
636917
Thank you. :) It works !
– tonymx227
Nov 23 '18 at 12:47
@tonymx227 not sure I'd be swallowing the internal errors as displayed here (and in your original code), the errors should be propagated up the stack and handled elsewhere or at least be logged better inline.
– James
Nov 23 '18 at 15:46
@James I did state that in the "Side note" below the code.
– Luke Stoward
Nov 26 '18 at 16:04
@LukeStoward you did, but as a bare minimum to ensure your code works e.g. your code doesn't propagate the error fromdb.queryso if that fails, the callstack is lost. Just emphasising the point to the OP that swallowing errors, in general, usually isn't a good idea.
– James
Nov 26 '18 at 16:17
@James Agree completely. I (perhaps wrongly) left the error handling logic out, since the example was already quite big. Hopefully, the OP read all of the solution and is handling errors.
– Luke Stoward
Nov 26 '18 at 16:50
add a comment |
In order for filePromise to contain a collection of promises, you need to return a promise for each iteration of your map call. Only then will the call to Promise.all be evaluated correctly.
var filePromise = _.map(files, function(file) {
return new Promise(function(resolve, reject) {
var filePath = './sql/' + file;
fs.lstat(filePath, function(err, stats) {
if (stats.isFile() && file !== '.gitignore' && file !== 'index.js') {
fs.readFile(filePath, 'utf-8', function(err, data) {
console.log('LOG 1');
db.query(data).then(function() {
console.log(colors.green('SUCCESS LOG 2'));
resolve();
}).catch(function() {
console.log(colors.red('ERROR LOG 2'));
reject();
});
console.log('LOG 3');
});
} else {
reject(new Error("failed condition"))
}
});
})
});
Promise.all(filePromise).then(function() {
console.log(colors.green('LOG 4'));
});
This does not fix the ordering of your console logs. That is a separate issue. Your console logs are not actually out of order, they are logging as expected. However, this is due to the async call you are making to db.query which, when triggered does not block waiting for a response. Instead the next line is executed immediately after the function call returns.
Side note: Make sure to handle your err arguments passed to the inline callback functions of fs.lstat and fs.readFile. Failure to do so will result in the promise never completing in the event of an error.
answered Nov 22 '18 at 14:51
Luke StowardLuke Stoward
636917
Thank you. :) It works !
– tonymx227
Nov 23 '18 at 12:47
@tonymx227 not sure I'd be swallowing the internal errors as displayed here (and in your original code), the errors should be propagated up the stack and handled elsewhere or at least be logged better inline.
– James
Nov 23 '18 at 15:46
@James I did state that in the "Side note" below the code.
– Luke Stoward
Nov 26 '18 at 16:04
@LukeStoward you did, but as a bare minimum to ensure your code works e.g. your code doesn't propagate the error fromdb.queryso if that fails, the callstack is lost. Just emphasising the point to the OP that swallowing errors, in general, usually isn't a good idea.
– James
Nov 26 '18 at 16:17
@James Agree completely. I (perhaps wrongly) left the error handling logic out, since the example was already quite big. Hopefully, the OP read all of the solution and is handling errors.
– Luke Stoward
Nov 26 '18 at 16:50
add a comment |
In order for filePromise to contain a collection of promises, you need to return a promise for each iteration of your map call. Only then will the call to Promise.all be evaluated correctly.
var filePromise = _.map(files, function(file) {
return new Promise(function(resolve, reject) {
var filePath = './sql/' + file;
fs.lstat(filePath, function(err, stats) {
if (stats.isFile() && file !== '.gitignore' && file !== 'index.js') {
fs.readFile(filePath, 'utf-8', function(err, data) {
console.log('LOG 1');
db.query(data).then(function() {
console.log(colors.green('SUCCESS LOG 2'));
resolve();
}).catch(function() {
console.log(colors.red('ERROR LOG 2'));
reject();
});
console.log('LOG 3');
});
} else {
reject(new Error("failed condition"))
}
});
})
});
Promise.all(filePromise).then(function() {
console.log(colors.green('LOG 4'));
});
This does not fix the ordering of your console logs. That is a separate issue. Your console logs are not actually out of order, they are logging as expected. However, this is due to the async call you are making to db.query which, when triggered does not block waiting for a response. Instead the next line is executed immediately after the function call returns.
Side note: Make sure to handle your err arguments passed to the inline callback functions of fs.lstat and fs.readFile. Failure to do so will result in the promise never completing in the event of an error.
answered Nov 22 '18 at 14:51
Luke StowardLuke Stoward
636917
In order for filePromise to contain a collection of promises, you need to return a promise for each iteration of your map call. Only then will the call to Promise.all be evaluated correctly.
var filePromise = _.map(files, function(file) {
return new Promise(function(resolve, reject) {
var filePath = './sql/' + file;
fs.lstat(filePath, function(err, stats) {
if (stats.isFile() && file !== '.gitignore' && file !== 'index.js') {
fs.readFile(filePath, 'utf-8', function(err, data) {
console.log('LOG 1');
db.query(data).then(function() {
console.log(colors.green('SUCCESS LOG 2'));
resolve();
}).catch(function() {
console.log(colors.red('ERROR LOG 2'));
reject();
});
console.log('LOG 3');
});
} else {
reject(new Error("failed condition"))
}
});
})
});
Promise.all(filePromise).then(function() {
console.log(colors.green('LOG 4'));
});
This does not fix the ordering of your console logs. That is a separate issue. Your console logs are not actually out of order, they are logging as expected. However, this is due to the async call you are making to db.query which, when triggered does not block waiting for a response. Instead the next line is executed immediately after the function call returns.
Side note: Make sure to handle your err arguments passed to the inline callback functions of fs.lstat and fs.readFile. Failure to do so will result in the promise never completing in the event of an error.
answered Nov 22 '18 at 14:51
Luke StowardLuke Stoward
636917
answered Nov 22 '18 at 14:51
Luke StowardLuke Stoward
636917
answered Nov 22 '18 at 14:51
Luke StowardLuke Stoward
636917
answered Nov 22 '18 at 14:51
Luke StowardLuke Stoward
636917
636917
Thank you. :) It works !
– tonymx227
Nov 23 '18 at 12:47
@tonymx227 not sure I'd be swallowing the internal errors as displayed here (and in your original code), the errors should be propagated up the stack and handled elsewhere or at least be logged better inline.
– James
Nov 23 '18 at 15:46
@James I did state that in the "Side note" below the code.
– Luke Stoward
Nov 26 '18 at 16:04
@LukeStoward you did, but as a bare minimum to ensure your code works e.g. your code doesn't propagate the error fromdb.queryso if that fails, the callstack is lost. Just emphasising the point to the OP that swallowing errors, in general, usually isn't a good idea.
– James
Nov 26 '18 at 16:17
@James Agree completely. I (perhaps wrongly) left the error handling logic out, since the example was already quite big. Hopefully, the OP read all of the solution and is handling errors.
– Luke Stoward
Nov 26 '18 at 16:50
add a comment |
Thank you. :) It works !
– tonymx227
Nov 23 '18 at 12:47
@tonymx227 not sure I'd be swallowing the internal errors as displayed here (and in your original code), the errors should be propagated up the stack and handled elsewhere or at least be logged better inline.
– James
Nov 23 '18 at 15:46
@James I did state that in the "Side note" below the code.
– Luke Stoward
Nov 26 '18 at 16:04
@LukeStoward you did, but as a bare minimum to ensure your code works e.g. your code doesn't propagate the error fromdb.queryso if that fails, the callstack is lost. Just emphasising the point to the OP that swallowing errors, in general, usually isn't a good idea.
– James
Nov 26 '18 at 16:17
@James Agree completely. I (perhaps wrongly) left the error handling logic out, since the example was already quite big. Hopefully, the OP read all of the solution and is handling errors.
– Luke Stoward
Nov 26 '18 at 16:50
Thank you. :) It works !
– tonymx227
Nov 23 '18 at 12:47
Thank you. :) It works !
– tonymx227
Nov 23 '18 at 12:47
@tonymx227 not sure I'd be swallowing the internal errors as displayed here (and in your original code), the errors should be propagated up the stack and handled elsewhere or at least be logged better inline.
– James
Nov 23 '18 at 15:46
@tonymx227 not sure I'd be swallowing the internal errors as displayed here (and in your original code), the errors should be propagated up the stack and handled elsewhere or at least be logged better inline.
– James
Nov 23 '18 at 15:46
@James I did state that in the "Side note" below the code.
– Luke Stoward
Nov 26 '18 at 16:04
@James I did state that in the "Side note" below the code.
– Luke Stoward
Nov 26 '18 at 16:04
@LukeStoward you did, but as a bare minimum to ensure your code works e.g. your code doesn't propagate the error from
db.query so if that fails, the callstack is lost. Just emphasising the point to the OP that swallowing errors, in general, usually isn't a good idea.– James
Nov 26 '18 at 16:17
@LukeStoward you did, but as a bare minimum to ensure your code works e.g. your code doesn't propagate the error from
db.query so if that fails, the callstack is lost. Just emphasising the point to the OP that swallowing errors, in general, usually isn't a good idea.– James
Nov 26 '18 at 16:17
@James Agree completely. I (perhaps wrongly) left the error handling logic out, since the example was already quite big. Hopefully, the OP read all of the solution and is handling errors.
– Luke Stoward
Nov 26 '18 at 16:50
@James Agree completely. I (perhaps wrongly) left the error handling logic out, since the example was already quite big. Hopefully, the OP read all of the solution and is handling errors.
– Luke Stoward
Nov 26 '18 at 16:50
add a comment |
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1
Your database query us async call. It will skip that block and begins next execution. You can use async/await or place your code inside of the then block of the query
– Sagar
Nov 22 '18 at 13:43
As @Sagar said, the execution does not pause at the
db.queryasync call. Instead once the async action has been triggered, the main thread will jump to the next line and continue execution.– Luke Stoward
Nov 22 '18 at 14:41