Develop Reference

How to disable method call if instance of object doesn't exist (javascript)

Is there a way to not call a method from the function object (instance of it) if that instance doesn't exist?
This is my function for sticky sidebar and it has 2 methods;
init() and updateSticky();
function stickySideBar(element, options = {}) {
var _this = this;
_this.init = function () {}
_this.updateSticky = function (timeout) {
//this is actually just a debouncer that calls init method
}
}
I want to use this updateSticky on window resize
$(window).on("resize", function () {
newsletterBlog.updateSticky();
sideBarBlog.updateSticky();
if ($(productsSticky.element).length > 0) {
productsSticky.updateSticky();
}
});
now I use if loop to check if an element exists but I would like to do that inside of the instance of that function
if i dont have if loop i get "Uncaught TypeError: e.updateSticky is not a function".
cheers
EDIT
here is the function
function stickySideBar(element, options = {}) {
var _this = this;
console.log("_this :>> ", _this);
//declared element
_this.debouncer;
_this.element = element;
if ($(_this.element).length === 0) {
return;
}
// declared options
_this.parentElementClass = options.parentElementClass;
_this.wrapClass = options.wrapClass;
_this.activeStickyClass = options.activeStickyClass;
_this.top = options.top;
_this.width = options.width;
_this.activeBottomClass = options.activeBottomClass;
_this.disableOnMobile = options.disableOnMobile ? options.disableOnMobile : true;
_this.breakpoint = 992;
_this.init = function () {
};
_this.updateSticky = function (timeout) {
if ($(_this.element).length === 0) return;
var timeoutVal = timeout ? timeout : 100;
clearTimeout(_this.debouncer);
_this.debouncer = setTimeout(function () {
_this.init();
}, timeoutVal);
};
return _this.init();
}

Javascript element.style.opacity is undefined. Why?

I am trying to make a JS function that flickers an element. I use a setInterval() for timing, but it gives the error message Uncaught TypeError: Cannot read property 'opacity' of undefined.
When I try to modify the opacity not with a timer, but "by hand", that works...
What am I doing wrong?
Usage:
document.getElementById('idOfTheElement').startFlicker();
The function:
Element.prototype.startFlicker = function() {
var blinkInterval = setInterval(function() {
if (parseInt(this.style.opacity) === 0) {
this.style.opacity = 1;
} else {
this.style.opacity = 0;
}
}, 50);
};

Try this
Element.prototype.startFlicker = function() {
var self = this;
var blinkInterval = setInterval(function() {
if (parseInt(self.style.opacity) === 0) {
self.style.opacity = 1;
} else {
self.style.opacity = 0;
}
}, 50);
};
In setInterval this refers to window, you need store context (this - current element) in variable and use in setInterval

Because of the context. this.style inside the setInterval refers to the global window object.

You could always make a reference to the element itself, because inside the setInterval function, the window object is passed as this.
Instead, you should give .bind() a try. So this will be a reference to the argument of the method.
Element.prototype.startFlicker = function() {
var blinkInterval = setInterval(function() {
if (parseInt(this.style.opacity) === 0) {
this.style.opacity = 1;
} else {
this.style.opacity = 0;
}
}.bind(this), 50);
};

Accessing a function within a function from outside in javascript

I have a nested function that I want to call from outside.
var _Config = "";
var tourvar;
function runtour() {
if (_Config.length != 0) {
tourvar = $(function () {
var config = _Config,
autoplay = false,
showtime,
step = 0,
total_steps = config.length;
showControls();
$('#activatetour').live('click', startTour);
function startTour() {
}
function showTooltip() {
}
});
}
}
function proceed() {
tourvar.showTooltip();
}
$(document).ready(function () {
runtour();
});
I was hoping to call it by tourvar.showTooltip(); but I seem to be wrong :) How can I make showTooltip() available from outside the function?

since my previous answer was really a hot headed one, I decided to delete it and provide you with another one:
var _Config = "";
var tourvar;
// Module pattern
(function() {
// private variables
var _config, autoplay, showtime, step, total_steps;
var startTour = function() { };
var showTooltip = function() { };
// Tour object constructor
function Tour(config) {
_config = config;
autoplay = false;
step = 0;
total_steps = _config.length;
// Provide the user with the object methods
this.startTour = startTour;
this.showTooltip = showTooltip;
}
// now you create your tour
if (_Config.length != 0) {
tourvar = new Tour(_Config);
}
})();
function proceed() {
tourvar.showTooltip();
}
$(document).ready(function () {
runtour();
});

function outerFunction() {
window.mynestedfunction = function() {
}
}
mynestedfunction();

Javascript callback managment

I'm having trouble with designing a class which exposes its actions through callbacks. Yes my approach works for me but also seems too complex.
To illustrate the problem I've drawn the following picture. I hope it is useful for you to understand the class/model.
In my approach, I use some arrays holding user defined callback functions.
....
rocket.prototype.on = function(eventName, userFunction) {
this.callbacks[eventName].push(userFunction);
}
rocket.prototype.beforeLunch = function(){
userFunctions = this.callbacks['beforeLunch']
for(var i in userFunctions)
userFunctions[i](); // calling the user function
}
rocket.prototype.lunch = function() {
this.beforeLunch();
...
}
....
var myRocket = new Rocket();
myRocket.on('beforeLunch', function() {
// do some work
console.log('the newspaper guys are taking pictures of the rocket');
});
myRocket.on('beforeLunch', function() {
// do some work
console.log('some engineers are making last checks ');
});
I'm wondering what the most used approach is. I guess I could use promises or other libraries to make this implementation more understandable. In this slide using callbacks is considered evil. http://www.slideshare.net/TrevorBurnham/sane-async-patterns
So, should I use a library such as promise or continue and enhance my approach?

var Rocket = function () {
this.timer = null;
this.velocity = 200;
this.heightMoon = 5000;
this.goingToMoon = true;
this.rocketStatus = {
velocity: null,
height: 0,
status: null
};
this.listener = {
};
}
Rocket.prototype.report = function () {
for (var i in this.rocketStatus) {
console.log(this.rocketStatus[i]);
};
};
Rocket.prototype.on = function (name,cb) {
if (this.listener[name]){
this.listener[name].push(cb);
}else{
this.listener[name] = new Array(cb);
}
};
Rocket.prototype.initListener = function (name) {
if (this.listener[name]) {
for (var i = 0; i < this.listener[name].length; i++) {
this.listener[name][i]();
}
return true;
}else{
return false;
};
}
Rocket.prototype.launch = function () {
this.initListener("beforeLaunch");
this.rocketStatus.status = "Launching";
this.move();
this.initListener("afterLaunch");
}
Rocket.prototype.move = function () {
var that = this;
that.initListener("beforeMove");
if (that.goingToMoon) {
that.rocketStatus.height += that.velocity;
}else{
that.rocketStatus.height -= that.velocity;
};
that.rocketStatus.velocity = that.velocity;
if (that.velocity != 0) {
that.rocketStatus.status = "moving";
}else{
that.rocketStatus.status = "not moving";
};
if (that.velocity >= 600){
that.crash();
return;
}
if (that.rocketStatus.height == 2000 && that.goingToMoon)
that.leaveModules();
if (that.rocketStatus.height == that.heightMoon)
that.landToMoon();
if (that.rocketStatus.height == 0 && !that.goingToMoon){
that.landToEarth();
return;
}
that.report();
that.initListener("afterMove");
that.timer = setTimeout(function () {
that.move();
},1000)
}
Rocket.prototype.stop = function () {
clearTimeout(this.timer);
this.initListener("beforeStop");
this.velocity = 0;
this.rocketStatus.status = "Stopped";
console.log(this.rocketStatus.status)
this.initListener("afterStop");
return true;
}
Rocket.prototype.crash = function () {
this.initListener("beforeCrash");
this.rocketStatus.status = "Crashed!";
this.report();
this.stop();
this.initListener("afterCrash");
}
Rocket.prototype.leaveModules = function () {
this.initListener("beforeModules");
this.rocketStatus.status = "Leaving Modules";
this.initListener("afterModules");
}
Rocket.prototype.landToMoon = function () {
this.initListener("beforeLandToMoon");
this.rocketStatus.status = "Landing to Moon";
this.goingToMoon = false;
this.initListener("afterLandToMoon");
}
Rocket.prototype.landToEarth = function () {
this.initListener("beforeLandToEarth");
this.stop();
this.rocketStatus.status = "Landing to Earth";
this.initListener("afterLandToEarth");
}
Rocket.prototype.relaunch = function () {
this.initListener("beforeRelaunch");
this.timer = null;
this.velocity = 200;
this.heightMoon = 5000;
this.goingToMoon = true;
this.rocketStatus = {
velocity: 200,
height: 0,
status: "relaunch"
};
this.launch();
this.initListener("afterRelaunch");
}
init;
var rocket = new Rocket();
rocket.on("afterLaunch", function () {console.log("launch1")})
rocket.on("afterLandToMoon", function () {console.log("land1")})
rocket.on("beforeLandToEarth", function () {console.log("land2")})
rocket.on("afterMove", function () {console.log("move1")})
rocket.on("beforeLaunch", function () {console.log("launch2")})
rocket.launch();
You can add any function before or after any event.
This is my solution for this kinda problem. I am not using any special methods anything. I was just wonder is there any good practise for this like problems. I dig some promise,deferred but i just can't able to to this. Any ideas ?

Looping functions with timeout

I want to have two functions (an animation downwards and animation upwards) executing one after the other in a loop having a timeout of a few seconds between both animations. But I don't know how to say it in JS …
Here what I have so far:
Function 1
// Play the Peek animation - downwards
function peekTile() {
var peekAnimation = WinJS.UI.Animation.createPeekAnimation([tile1, tile2]);
// Reposition tiles to their desired post-animation position
tile1.style.top = "-150px";
tile2.style.top = "-150px";
peekAnimation.execute();
}
Function 2
// Play the Peek animation - upwards
function unpeekTile() {
var peekAnimation = WinJS.UI.Animation.createPeekAnimation([tile1, tile2]);
// Reposition tiles to their desired post-animation position
tile1.style.top = "0px";
tile2.style.top = "0px";
peekAnimation.execute();
}
And here's a sketch how both functions should be executed:
var page = WinJS.UI.Pages.define("/html/updateTile.html", {
ready: function (element, options) {
peekTile();
[timeOut]
unpeekTile();
[timeOut]
peekTile();
[timeOut]
unpeekTile();
[timeOut]
and so on …
}
});

You can do this using setTimeout or setInterval, so a simple function to do what you want is:
function cycleWithDelay() {
var delay = arguments[arguments.length - 1],
functions = Array.prototype.slice.call(arguments, 0, arguments.length - 1),
pos = 0;
return setInterval(function () {
functions[pos++]();
pos = pos % functions.length;
}, delay);
}
Usage would be like this for you:
var si = cycleWithDelay(peekTile, unpeekTile, 300);
and to stop it:
clearInterval(si);
This will just cycle through the functions calling the next one in the list every delay msec, repeating back at the beginning when the last one is called. This will result in your peekTile, wait, unpeekTile, wait, peekTile, etc.
If you prefer to start/stop at will, perhaps a more generic solution would suit you:
function Cycler(f) {
if (!(this instanceof Cycler)) {
// Force new
return new Cycler(arguments);
}
// Unbox args
if (f instanceof Function) {
this.fns = Array.prototype.slice.call(arguments);
} else if (f && f.length) {
this.fns = Array.prototype.slice.call(f);
} else {
throw new Error('Invalid arguments supplied to Cycler constructor.');
}
this.pos = 0;
}
Cycler.prototype.start = function (interval) {
var that = this;
interval = interval || 1000;
this.intervalId = setInterval(function () {
that.fns[that.pos++]();
that.pos %= that.fns.length;
}, interval);
}
Cycler.prototype.stop = function () {
if (null !== this.intervalId) {
clearInterval(this.intervalId);
this.intervalId = null;
}
}
Example usage:
var c = Cycler(peekTile, unpeekTile);
c.start();
// Future
c.stop();

You use setInterval() to call unpeekTile() every 1000 milliseconds and then you call setTimeOut() to run peekTile() after 1000 milliseconds at the end of the unpeekTile() function:
function peekTile() {
var peekAnimation = WinJS.UI.Animation.createPeekAnimation([tile1, tile2]);
// Reposition tiles to their desired post-animation position
tile1.style.top = "-150px";
tile2.style.top = "-150px";
peekAnimation.execute();
}
function unpeekTile() {
/* your code here */
setTimeout(peekTile, 1000);
}
setInterval(unpeekTile, 1000);

Check out the fiddle
var animation = (function () {
var peekInterval, unpeekInterval, delay;
return {
start: function (ip) {
delay = ip;
peekInterval = setTimeout(animation.peekTile, delay);
},
peekTile: function () {
//Your Code goes here
console.log('peek');
unpeekInterval = setTimeout(animation.unpeekTile, delay);
},
unpeekTile: function () {
//Your Code goes here
console.log('unpeek');
peekInterval = setTimeout(animation.peekTile, delay);
},
stop: function () {
clearTimeout(peekInterval);
clearTimeout(unpeekInterval);
}
}
})();
animation.start(1000);
// To stop
setTimeout(animation.stop, 3000);
​
I can't use this instead of animation.peekTile as setTimeout executes in global scope