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Why doesn't the removeChild remove the element?

I have written this scrip to take out ads on a website. Was working on it the whole day.
This is the JS code:
var timer = setInterval(deletor, 1);
function deletor() {
timer;
var slider = document.querySelector("#slider-con");
var bannerTop = document.querySelector("#MainContent > div:nth-child(2)")
var bannerMiddle = document.querySelector("#MainContent > iframe");
var bannerRandom = document.querySelector("#MainContent > div:nth-child(7)");
var bannerRandom2 = document.querySelector("#MainContent > div:nth-child(6)");
if (slider == undefined) {
return false;
} else {
slider.parentNode.removeChild(slider);
};
if (bannerTop == undefined) {
return false;
} else {
bannerTop.parentNode.removeChild(bannerTop);
};
if (bannerMiddle == undefined) {
return false;
} else {
bannerMiddle.parentNode.removeChild(bannerMiddle);
};
if (bannerRandom == undefined) {
return false;
} else {
bannerRandom.parentNode.removeChild(bannerRandom);
};
if (bannerRandom2 == undefined) {
return false;
} else {
bannerRandom2.parentNode.removeChild(bannerRandom2);
};
};
Now, as you can see, it gets the values first and then goes through if statements. Idea behind this is: On first try, it deletes the elements and on the second one, it stops the function.
But when I inserted this last element, it won't delete it. The ID is correct, everything is correct but it won't delete the element, so I keep getting the same alert over and over.
Also, I found out that, I get this banner ad on two places. When I have "var bannerRandom = document.querySelector("#MainContent > div:nth-child(7)");" this, it appears as "document.querySelector("#MainContent > div:nth-child(6)")" this, and when I have both, it appears as "document.querySelector("#MainContent > div:nth-child(6)")" this. And it's not deleted.
Console shows no errors.

Your various statements in the form:
if (slider == undefined) {
return false;
} else {
slider.parentNode.removeChild(slider);
};
mean this: "If slider wasn't found in the DOM, exit the function. Otherwise, remove the slider and continue the function."
So that means your function will terminate the first time one of the elements you're looking for doesn't exist. Since it terminates then, none of the other elements after it is checked. That seems unlikely to be what you want to do.
You probably just wanted:
if (slider) {
slider.parentNode.removeChild(slider);
}
...and so on.
Note that you don't put ; at the end of a block attached to a flow-control statement like if or else, which is why I've removed it above. (Doing so is harmless, because JavaScript ignores them; but it's pointless.)

how to make alerts appear if the number of infant is more than adults

I want to make the alert appear if the number of infant is more than adults.
I've tried but it looks like something went wrong.
Please help.. thanks before
ex: http://jsfiddle.net/pBxfX/132/
var button = $('#submit'),
adult = $('#adult option:selected').val(),
infant = $('#infant option:selected').val();
if(adult > infant) {
$("#alert").hide;
}
else if(adult == infant) {
$("#alert").hide;
}
else {
$("#alert").show;
}

A few things:
You need to treat hide and show as methods (call them as .hide() and .show())
You need to execute your checking code in the change event handler for the select.
When comparing adults to infants, you need to treat them as integers (they are currently being treated as strings).
See http://jsfiddle.net/pBxfX/133/ for updated code
var button = $('#submit');
$(document).ready(function() {
$(button).attr('disabled', true);
$('input[type="text"]').on('keyup', function() {
var from = $("#from").val(),
to = $("#to").val();
if (from != '' && to != '') {
$(button).attr('disabled', false);
} else {
$(button).attr('disabled', true);
}
});
// Run code when any <select> changes
$("select").on('change', function() {
var adult = parseInt($('#adult option:selected').val()); //convert to integers for comparison
var infant = parseInt($('#infant option:selected').val()); //convert to integers for comparison
if (adult > infant) {
$("#alert").hide(); //Note that it is .hide() not .hide
} else if (adult == infant) {
$("#alert").hide();
} else {
$("#alert").show();
}
});
});

hide() and show() are functions so you need to add () to call these functions.
if(adult > infant) {
$("#alert").hide();
}
else if(adult == infant) {
$("#alert").hide();
}
else {
$("#alert").show();
}

Jquery keydown only works once

EDIT: I solved it by changing = to ==, but that didnt fully solve it but then I added a change to $currentSlide and now it works! Yay!
$(document).keydown(function(e) {
if(e.keyCode == 39)
{
if($currentSlide == $slide1){
slideShow(slide2);
$currentSlide = $slide2;
}
else if($currentSlide == $slide2){
slideShow(slide3);
$currentSlide = $slide3;
}
else if($currentSlide == $slide3){
slideShow(slide1);
$currentSlide = $slide1;
}
}
})
I have searched for an answer but haven't found anything that suits my question. I am a noob on javascript so bear with me.
I have a function that works as a slideshow. (I use $ in front of my jquery variables, I have a lot of javascript variables too so I just use it to separate them.)
var $currentSlide = "#slide1";
var $slide1 = "#slide1";
var $slide2 = "#slide2";
var $slide3 = "#slide3";
function slideShow($slide) {
if ($slide != $currentSlide){
$($currentSlide).fadeOut(500);
$($slide).delay(500).fadeIn(500);
$currentSlide = $slide;
}
};
To call this function, I use a simple link with parameter depending on which slide is active.
onclick="slideShow(slide2)"
And then I want to change slide with keypress (to right). This is my code for the keypress:
$(document).keydown(function(e) {
if(e.keyCode == 39) {
if ($currentSlide = $slide1){
slideShow(slide2);
} else if($currentSlide = $slide2) {
slideShow(slide3);
} else if($currentSlide = $slide3) {
slideShow(slide1);
}
}
})
It works perfectly when using the links but when I press key it behaves very weird. First click works like a charm, but then it doesnt work any more. If I click to get the third slide, another click will put next slide on top of slide3 but slide3 never goes away.
I realise there is some huge mistake by me here but I'm too much of a beginner to fix it. Any ideas?

your if-else conditions will always be true, because you used '=' instead of '=='. since your first if condition will be true it always shows slide2 and it looks to you that it only worked once
$(document).keydown(function(e) {
if(e.keyCode == 39) {
if ($currentSlide == $slide1){
slideShow(slide2);
} else if($currentSlide == $slide2) {
slideShow(slide3);
} else if($currentSlide == $slide3) {
slideShow(slide1);
}
}
})
The second problem maybe caused by the clock on the slideshow, if you are using one. When you click the next/previous button you need to reset the clock of your slideshow.

There are two issues
You do an assignment in your if conditions, so they always are true. Instead use the comparator ===;
In the onclick attribute you specify an undefined variable, since the $ is missing from it
Beside correcting this, I would suggest to use a class for your slide elements, not individual IDs. So use class="slide" instead of id="slide1" in your HTML, and apply it to all slides -- they can share the same class.
Then store the sequence number of the current slide, counting from 0.
I would also remove all the onclick attributes on the slide elements and deal with click handlers from code, which can be done quite concisely with $('.slide').click( ... ):
var currentSlideNo = 0; // zero-indexed
function slideShow(slideNo) {
if(slideNo != currentSlideNo){
$('.slide').get(currentSlideNo).fadeOut(500);
currentSlideNo = slideNo;
$('.slide').get(currentSlideNo).delay(500).fadeIn(500);
}
};
$('.slide').click(function () {
slideShow((currentSlideNo + 1) % $('.slide').length);
});
$(document).keydown(function(e) {
if (e.keyCode == 39) {
slideShow((currentSlideNo + 1) % $('.slide').length);
}
});

jQuery.css('display') only returns inline

I am trying to get checked options from a table which are set inline. There is a search function, which sets $(element).css('display','none') on objects in which there is no match with the search. Anyways, this piece of code will only return inline, no matter what the elements are set to. Even if I manually set all of them to display: none in the table itself, the alert will return inline for every single object in the table. Is there any solution to this?
JS code:
function pass_QR() {
var i = 0;
var array = [];
$("input:checkbox:checked").each(function () {
i++;
alert($(this).css('display'));
if ($(this).val() !== 0 && $(this).css('display') === 'inline') {
array.push($(this).val());
}
});
}

Fundamentally, css("display") does work, so something else is going on.
I suspect one of two things:
The checkboxes that you're making display: none are never checked, and so you don't see them in your each loop.
You're not making the checkboxes display: none, but instead doing that to some ancestor element of them. In that case, $(this).is(":visible") is what you're looking for.
Here's an example of #2: Live Copy | Live Source
<div id="ancestor">
<input type="checkbox" checked>
</div>
<script>
$("#ancestor").css("display", "none");
console.log("display property is now: " +
$("input:checkbox:checked").css("display"));
console.log("visible tells us what's going on: " +
$("input:checkbox:checked").is(":visible"));
</script>
...which outputs:
display property is now: inline-block
visible tells us what's going on: false
Applying that to your code:
function pass_QR() {
var i = 0;
var array = [];
$("input:checkbox:checked").each(function () {
i++;
alert($(this).css('display'));
if ($(this).val() !== 0 && $(this).is(':visible')) {
// Change is here -----------------^^^^^^^^^^^^^^
array.push($(this).val());
}
});
}
Side note: Every time you call $(), jQuery has to do some work. When you find yourself calling it repeatedly in the same scope, probably best to do that work once:
function pass_QR() {
var i = 0;
var array = [];
$("input:checkbox:checked").each(function () {
var $this = $(this); // <=== Once
i++;
alert($this.css('display'));
if ($this.val() !== 0 && $this.is(':visible')) {
// Other change is here -------^^^^^^^^^^^^^^
array.push($this.val());
}
});
}

try following:
$("input:checkbox:checked").each(function(i,o){
console.log($(this).css("display"));
});
working fiddle here: http://jsfiddle.net/BcfvR/2/

Modifying HTML elements using jquery

I am trying to use jquery to add and remove a class from <li> elements according to a variable's value ( i ).
Here is a jsfiddle of what I have done so far http://jsfiddle.net/LX8yM/
Clicking the "+" increments i by 1 ( I have checked this with chrome's javascript console ).
One should be able to click "+" and the class .active should be removed from and added to the <li> elements accordingly.
...I can get the first <li> element to accept the class, that's all...

No need for if statements:
$(document).ready(function (){
$('#add').click(function (){
$('.numbers .active').removeClass('active').next().addClass('active');
});
});
jsfiddle
Do note that I added an 'active' class to first list item. You could always do this via JS if you do not have control over the markup.

Your if..else.. is hanging in document.ready. Wrap the increment inside a function and call it respectively.
Like
$(document).ready(function (){
//variable
var i = 1;
//if statments
function incre(i){ // wrap into a function and process it
if(i == 1){
$('#one').addClass('active');
$('#two').removeClass('active');
$('#three').removeClass('active');
}else if(i == 2){
$('#one').removeClass('active');
$('#two').addClass('active');
$('#three').removeClass('active');
}else if(i == 3){
$('#one').removeClass('active');
$('#two').removeClass('active');
$('#three').addClass('active');
}
}
//change i
$('#add').click(function (){
incre(i++); // pass it as a parameter
});
});
Working JSFiddle

This would be easier:
$(document).ready(function(){
var i = 0; // set the first value
$('#something').click(function(){
i++; // every click this gets one higher.
// First remove class, wherever it is:
$('.classname').removeClass('classname');
// Now add where you need it
if( i==1){
$('#one').addClass('classname');
} else if( i==2){
$('#two').addClass('classname');
} else if( i==3){
$('#three').addClass('classname');
}
}):
});

See this code. Initially you have to add class to one.
$(document).ready(function (){
//variable
var i = 1;
$('#one').addClass('active');
//if statments
//change i
$('#add').click(function (){
i++;
if(i == 1){
$('#one').addClass('active');
$('#two').removeClass('active');
$('#three').removeClass('active');
}else if(i == 2){
$('#one').removeClass('active');
$('#two').addClass('active');
$('#three').removeClass('active');
}else if(i == 3){
$('#one').removeClass('active');
$('#two').removeClass('active');
$('#three').addClass('active');
}
});
});

It's being called only once, not in the click event function. This edit of your fiddle works: http://jsfiddle.net/LX8yM/2/
put it in the
'$('#add').click(function (){}'