Develop Reference

How to compare executed function output correctly?

So what im trying to do in general is -> get a moment when user scrolls up really fast on mobile device -> some text executed in console (for example)
What I have is 2 simple functions:
//calculate scroll speed
var mobileScroll = (function(){
var last_position, new_position, timer, delta, delay = 50;
function clear() {
last_position = null;
delta = 0;
}
clear();
return function(){
new_position = window.scrollY;
if ( last_position !== null ){
delta = new_position - last_position;
}
last_position = new_position;
clearTimeout(timer);
timer = setTimeout(clear, delay);
return delta;
};
})();
Then I'm trying to compare the outputted value with some static number like this:
var scrolledFast = function scrolledFast(e) {
console.log("scroll: " + mobileScroll());//works fine
console.log(mobileScroll());//always 0
//if statement does not work
if(document.body.classList.contains('on-mobile-device') && mobileScroll() < -200 ){
console.log('Scrolled up fast enough');
}
}
document.addEventListener('scroll', scrolledFast);
The problem is that I don't understand why I can get the outputted value like this:
console.log("scroll speed: " + mobileScroll()); // I see "scroll: -100" or some other value
But when I'm trying to get something like:
console.log(mobileScroll());
//or
var mobScrollSpeed = mobileScroll();
console.log(mobScrollSpeed);
it is always 0...

Dom element infinitely incrementing

I'm in my first steps of creating an auto aim system for the enemy bot but I can't even seem to get him to shoot properly.
I create a div element, and move it in a direction. This happens every 4 seconds. I delete the div before the next one gets created. This works. But somehow it creates more and more elements over time and soon turns into a massive amount of divs all flying in the same direction.
** make the bullet here **
function makeBullet() {
if (player.enemy) {
if (player.enemyBullet.bulletInterval == true) {
console.log("working");
player.enemyBullet.bullet = document.createElement('div');
player.enemyBullet.bullet.className = 'bullet';
gameArea.appendChild(player.enemyBullet.bullet);
player.enemyBullet.bullet.x = player.enemy.x;
player.enemyBullet.bullet.y = player.enemy.y;
player.enemyBullet.bullet.style.left = player.enemyBullet.bullet.x + 'px';
player.enemyBullet.bullet.style.top = player.enemyBullet.bullet.y + 'px';
player.enemyBullet.bulletInterval = false;
setInterval(function () {
player.enemyBullet.bulletInterval = true;
}, 4000);
}
}
}
** Move Bullet **
function moveBullet() {
let bullets = document.querySelectorAll('.bullet');
bullets.forEach(function (item) {
item.x += 3;
item.y -= 3;
item.style.left = item.x + 'px';
item.style.top = item.y + 'px';
if(item.y < 200){
item.parentElement.removeChild(item);
player.enemyBullet.bullet = null;
}
})
}
** invoked in request Animation function **
function playGame() {
if (player.inplay) {
moveBomb();
moveBullet();
makeBullet();
window.requestAnimationFrame(playGame);
}
}
** Initiate interval boolean here **
let player = {
enemyBullet: {
bulletInterval: true
}
}
** LINK TO JS FIDDLE FULL PROJECT ** (click here to see what's happening)
https://jsfiddle.net/mugs17/j7f12a0n/

You are using setInterval like set timeout. However setInterval does not only execute one time. Once you've called setInterval the first time, calling it again makes a new different interval that also executes every 4 seconds.
So each time your function gets invoked its creating a new Interval which is why your div elements are increasing as time goes on
Instead wrap the entire create bullet code inside setInterval and make it execute only once by setting a boolean conditional and then immediately changing that conditional to false. Like this:
if (player.enemy) {
if (player.enemyBullet.bulletInterval == true) {
player.enemyBullet.bulletInterval = false;
console.log("working");
setInterval(function () {
player.enemyBullet.bullet = document.createElement('div');
player.enemyBullet.bullet.className = 'bullet';
gameArea.appendChild(player.enemyBullet.bullet);
player.enemyBullet.bullet.x = player.enemy.x;
player.enemyBullet.bullet.y = player.enemy.y;
player.enemyBullet.bullet.style.left = player.enemyBullet.bullet.x + 'px';
player.enemyBullet.bullet.style.top = player.enemyBullet.bullet.y + 'px';
}, 4000);
}
}
}

Does alert('some message') can make an impact in a callback function - Javascript

I had written a callback function to capture the snapshot of running video using html5 video control and canvas.
I used a for loop to iterate and call the same callback function take the burst capture. If i add alert('') in the callback , the video in the background rerendering when alert message display, the burst snap shot works fine as taking diff photos(frames/images of the running video). But when I removed the alert('') , the video does not run in the background and the bursted images are the same instead of different.
The code
for (var i = 0; i < burstcount; i++) {
var wcam = Webcam;
wcam.burst_snap(function (dataurl, id) {
var arrayindex = passedName + "_" + id;
imgid = imgid + i;
alert(dataurl);
burstcapturedata[arrayindex] = dataurl;
}, i);
var j = 0;
while (j < 10000000000) {
j++;
}
}
DisplayBurstedImages();
}

Yes, actually. Alert holds next execution of code. If your code works with alert it means that you require delay.
Try setTimeout or put the code in the correct place where everything is getting loaded.

I guess it needs time for binding video. you can use setTimeout function for delay.
var delay =100;
setTimeout(function () {/*your function*/ }, delay);
delay = delay + 300;

Your code needs to look something like this:
var wcam = Webcam;
var cnt = 0;
wcam.burst_snap(function(dataurl, id) {
var arrayindex = passedName + "_" + id; //you do not have an array if this is the key
imgid = imgid + cnt; //no clue what this is for
cnt++;
burstcapturedata[arrayindex] = dataurl;
if (cnt===burstcount) {
DisplayBurstedImages();
}
}, 100); //no clue what that value is supposed to be

Javascript gradual width increase

I'm trying to gradually increase the elements of 2 id's in javascript using a Timeout. I can get one working but when trying to call another element into the same function it only does one iteration then crashes after the first recursive call.
I'm passing two id's for the elements. and I want the left element to gradually increase while the right element gradually increases in width.
Heres what ive got
function grow(elementL, elementR)
{
var htL = parseInt(document.getElementById(elementL).style.width,10);
var htR = parseInt(document.getElementById(elementR).style.width,10);
var movementL = htL + 5;
var movementR = htR - 5;
document.getElementById(elementL).style.width = movementL + 'px';
document.getElementById(elementR).style.width = movementR + 'px';
if (movementL > 1000) {
clearTimeout(loopTimer);
return false;
}
var loopTimer = setTimeout('grow(\''+elementL+','+elementR+'\')',50);
}

You could simplify this (removing the script-generation) by using setInterval -- this repeats the function call until you cancel it.
function grow(elementL, elementR)
{
var loopTimer = setInterval(function() {
if (!growStep(elementL, elementR)) {
clearInterval(loopTimer);
}
}, 50);
}
function growStep(elementL, elementR) {
var htL = parseInt(document.getElementById(elementL).style.width,10);
var htR = parseInt(document.getElementById(elementR).style.width,10);
var movementL = htL + 5;
var movementR = htR - 5;
document.getElementById(elementL).style.width = movementL + 'px';
document.getElementById(elementR).style.width = movementR + 'px';
if (movementL > 1000) {
return false;
}
return true;
}
(Fiddle)
Edit
Yeah, I guess the only problem with the OP code is that it passes a string to setTimeout, rather than the function itself:
var loopTimer = setTimeout(function() {
grow(elementL, elementR);
},50);

setTimeout('grow(\''+elementL+','+elementR+'\')',50)
would need to be
setTimeout('grow(\''+elementL+'\',\''+elementR+'\')',50)
// ^^ ^^
to work. But don't do that. Pass a function expression to setTimeout:
setTimeout(function() {
grow(elementL, elementR);
}, 50)

Setting a time for flicker animation on img

I'm using this code to make my logo flicker on my website. But It becomes annoying when it continues to flicker while browsing, how can I set a time to allow it to flicker for something like the first 15seconds on page load, then stops?
JS code I'm using:
$(document).ready(
function(){
var t;
const fparam = 100;
const uparam = 100;
window.flickr = function(){
if(Math.round(Math.random())){
$("#logodcoi").css("visibility","hidden");
t = setTimeout('window.unflickr()',uparam);
}
else
t = setTimeout('window.flickr()',fparam);
}
window.unflickr = function(){
if(Math.round(Math.random())){
$("#logodcoi").css("visibility","visible");
t = setTimeout('window.flickr()',fparam);
}
else
t = setTimeout('window.unflickr()',uparam);
}
t = setTimeout('window.flickr()',fparam);
});

You could have a counter, which you then use to decide whether you want to set another timeout. As a side note, you should never add functions to window and then passing a string to setTimeout. Always just pass the function itself:
$(document).ready(function(){
var t;
var amount = 0;
const fparam = 100;
const uparam = 100;
function timeout(f, t) { // this function delegates setTimeout
if(amount++ < 150) { // and checks the amount already (un)flickered
setTimeout(f, t); // (150 * 100 ms = 15 s)
}
}
var flickr = function(){
if(Math.round(Math.random())){
$("#logodcoi").css("visibility","hidden");
t = timeout(unflickr,uparam);
}
else
t = timeout(flickr,fparam);
};
var unflickr = function(){
if(Math.round(Math.random())){
$("#logodcoi").css("visibility","visible");
t = timeout(flickr,fparam);
}
else
t = timeout(unflickr,uparam);
};
t = timeout(flickr,fparam);
});

I see you're using jquery, you could use the following, if I remember correctly, all the stuff I use below has been in jquery since 1.0, so you should be good:
counter = 1;
function hideOrShow(){
$(".classToSelect").animate({"opacity": "toggle"}, 100);
counter = counter +1;
if (counter >= 21) clearInterval(flickerInterval);
}
flickerInterval = setInterval(hideOrShow, 100);
Change the selector, animation duration, and variable names to whatever you fancy/need.