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getting NaN when asking for video duration [closed]

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Can anyone help me understand why console.log(this.getPlayerDuration()) inside of setAttendancePromptTimeLimit() is returning NaN?
// video-player.js
const videoP = document.querySelector('#in-course-player')
class videoPlyer {
constructor(videoElem){
this.vidPlayer = videoElem
}
play = function(cb){
arguments.length ? cb : console.log('play')
}
addListener = (elem, event, cb) => {
elem.addEventListener(event, cb)
}
getPlayerCurrentTime = () => this.vidPlayer.currentTime
getPlayerDuration = () => this.vidPlayer.duration
showVideoDuration = function(cb){
arguments.length ? cb : this.addListener(this.vidPlayer, 'loadedmetadata', () =>
console.log(this.getPlayerDuration()))
}
setAttendancePromptTimeLimit = cb => {
// returns NAN
console.log(this.getPlayerDuration())
}
init = () => {
//returns 16.1
this.showVideoDuration()
//returns NAN
this.setAttendancePromptTimeLimit()
}
}
const coursePlayer = new videoPlyer(videoP)
coursePlayer.init()

[...] If no media data is available, the value NaN is returned. [...]
https://developer.mozilla.org/en-US/docs/Web/API/HTMLMediaElement/duration

What is the correct way to make validations in JS, using the IF control structure [closed]

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I want to know which control structure to handle validations is better
I tried with if else if, and if -> return... if -> return
Which is better and more understandable?
if(user.name == null) {
errorMessage ('insert name')
} else if (user.age == null) {
errorMessage('Insert age')
} else {
insertUser(user)
}
OR
if(user.name == null) {
errorMessage ('insert name')
return
}
if (user.age == null) {
errorMessage('Insert age')
return
}
insertUser(user)

These are not equivalent, so it's not a matter of which one is better style.
What will happen if name is null and age is also null if you use the first code block? Answer: you will only set the name, and the age will remain null.
So you should use the second block.
Also, instead of the check if (a == null) you should generally consider using something like if (!a). This handles not only null values but also a few more falsy values (e.g. undefined, '', etc.).

The better way would be to collect all the errors first. Then check if you have any errors and finally insert a user if no errors are found.
const errors = ['name', 'age'].forEach( field => {
if(user[field] === null) {
return `${field} is required`
}
})
if (errors.length === 0) {
insertUser(user)
} else {
showErrors(errors)
}

In terms of performance, they are the same.
Regarding code readability, I prefer the later.
For maintenance, the later, as you may want later a list of all errors and it will be easier to implement.
How about:
try {
check(user.name, 'insert name');
check(user.age, 'insert age');
...
insertUser(user);
} catch(e) {
// handle e
}
const check = (value, message) => {
if (!value) {
throw `${message}`;
}
};

j-query showing syntax error [closed]

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Closed 8 years ago.
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i have a slider its not auto-play when i use this j-query code its showing syntax error. But i did'nt find syntax error. Please help
jQuery(document).ready(function () {
var photoslider = new WallopSlider('.photo-slider');
//autoplay
var count = photoslider.allItemsArrayLength;
var start = photoslider.currentItemIndex;
var end = count + 1;
var index = start;
jQuery(function () {
setInterval(function () {
photoslider.goTo(index);
++index;
if (index == end) {
index = start
}
}, 3000);
});

Please put }); after your coding

You forget to put the closing curly braces and parenthesis of jQuery(document).ready(function() {. Which is })

jQuery(document).ready(function () {
var photoslider = new WallopSlider('.photo-slider');
//autoplay
var count = photoslider.allItemsArrayLength;
var start = photoslider.currentItemIndex;
var end = count + 1;
var index = start;
jQuery(function () {
setInterval(function () {
photoslider.goTo(index);
++index;
if (index == end) {
index = start
}
}, 3000);
});
}); //--> this is missing

print a for-loop in the console log inside an if-statement [closed]

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Here is my code, and the JSFiddle.
I can't make the code work and I think it is because the if-statement that includes a for loop inside.
How can I make the whole code work, I've tried it with 4 different code possibilities and none of them worked/
var commands = {
'BOH': {
text: 'BOH!',
},
'HALO': {
text: 'HALO!',
},
'help()': {
text: 'Please press F12 and see the value list.',
},
};
$(".code").on("click", function () {
var codePrompt = prompt("enter the value"),
command = commands[codePrompt],
alertMessage = "";
consoleMessage = "Used '" + codePrompt + "' value.";
if(!command) {
alertMessage = "We are sorry but you entered a WRONG value.";
} else {
alertMessage = command.text;
};
if(command == 'help()') {
for (key in commands){
console.log(commands[key]);
alertMessage = command.text;
};
};
alert(alertMessage);
console.log(consoleMessage);
});

Shouldn't this
if(command == 'help()') {
be
if(codePrompt == 'help()') {

Node, RSVP.js array of promises [closed]

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i can get the RSVP array of promises to work:
//if user wants to change username
var promises = [];
promises['username'] = new RSVP.Promise(function(resolve, reject){
if(user.username !== session.username){
//check if username is available
$model_users.getBy({
what:'id',
where: " username = "+db.escape(user.username) +" AND id != "+ db.escape(session.id_user)
})
.then(function(results){
if(!results || results.length <= 0){
//update username is available
$model_users.update({
update:{username: db.escape(user.username)},
where: " id = "+ db.escape(session.id_user)
})
.then(function(success){
confirm.username = 'was_saved';
resolve(success);
},function(err){
reject(err);
console.log('db-error 55299 ' + err);
res.send('db-error');
});
}else{
validation.username = 'error_username_exists';
resolve(validation);
res.send({"validation":validation});
}
},function(err){
reject(err);
console.log('db-error 0299 ' + err);
res.send('db-error');
});
}else{
reject('no username to update - is same to session username');
}
}
//create new JWT and send it back to FE localSTorage
RSVP.all(promises).then(function(){
$model_users.getBy({
what:'id , username',
where: " id = "+ db.escape(session.id_user)
}).then(function(results){
if(results && results.length > 0){
//set new user session and token
var auth = {};
auth.username = results[0].username;
auth.id_user = results[0].id;
auth.session_token = jwt.sign(auth, config.session_secret_key, { expiresInMinutes: config.session_expiration });
res.send({"auth":auth,"confirm":confirm});
}else{
res.send('db-error');
}
},function(err){
console.log('db-error 0.577 '+ err);
});
});
the error returned is:
RSVP.all(promises).then(function(){
^^^^
SyntaxError: Unexpected identifier
How is his possible? i'm following the official doc https://github.com/tildeio/rsvp.js/#arrays-of-promises
I setted it on top of node app.js :
var RSVP = require('rsvp');

You're missing a ) two lines above RSVP.all(promises)....
Consider using a linter, which will catch this sort of error immediately. See e.g. SublimeLinter.