I have a javascript function for a slider in the JS file of my site. When we are in a page where the slider is not called or there is no trigger element, it displays an error in the console "Uncaught TypeError: Cannot read properties of null (reading ‘querySelector’) ", This error is not displayed when the slider is in the page.
I would like to know how to avoid this error, and how to prevent this function from loading in pages where this slider is not present?
function slider(set) {
const sliderContainer = document.querySelector(set.name),
slider = sliderContainer.querySelector('.slider'),
sliderItem = slider.querySelectorAll('.slider__item'),
sliderArrows = sliderContainer.querySelectorAll('.arrows__item');
let dotsCreate,
dotsClass,
dotsFunk,
numberSlider,
numberSliderWork,
sliderExecutionLine,
sliderExecutionLineWork;
// calculate the maximum width of all slides
function forSliderItem(t) {
t = 0;
for(let i = 0; i < sliderItem.length - 1; i++) {
t += sliderItem[i].clientWidth;
}
return t;
}
let maxWidth = forSliderItem(sliderItem), // maximum width of all slides
slidWidth = 0, // main variable for calculating the movement of the slider
count = 0; // counter
//===== flip left
sliderArrows[0].addEventListener('click', function() {
if(count !== 0) {
count--;
slidWidth -= sliderItem[count].clientWidth;
slider.style.transform = `translateX(-${slidWidth}px)`;
} else {
count = sliderItem.length - 1;
slidWidth = maxWidth;
slider.style.transform = `translateX(-${slidWidth}px)`;
}
if(set.dots) {
dotsFunk();
}
if(set.numberSlid) {
numberSliderWork(count);
}
if(set.line) {
sliderExecutionLineWork(count);
}
});
//===== flip right
sliderArrows[1].addEventListener('click', function() {
if(count < sliderItem.length - 1) {
count++;
slidWidth += sliderItem[count].clientWidth;
slider.style.transform = `translateX(-${slidWidth}px)`;
} else {
count = 0;
slidWidth = 0;
slider.style.transform = `translateX(-${slidWidth}px)`;
}
if(set.dots) {
dotsFunk();
}
if(set.numberSlid) {
numberSliderWork(count);
}
if(set.line) {
sliderExecutionLineWork(count);
}
});
//===== dots
if(set.dots) {
dotsCreate = function() {
const dotContainer = document.createElement('div'); // create dots container
dotContainer.classList.add('dots');
// create the required number of dots and insert a container into the dots
sliderItem.forEach(() => {
let dotsItem = document.createElement('span');
dotContainer.append(dotsItem);
});
sliderContainer.append(dotContainer);
};
dotsCreate();
// add the class to the desired dots, and remove from the rest
dotsClass = function(remove, add) {
remove.classList.remove('dots_active');
add.classList.add('dots_active');
};
// move slides by clicking on the dot
dotsFunk = function() {
const dotsWork = sliderContainer.querySelectorAll('.dots span'); // we get dots
dotsWork.forEach((item, i) => {
dotsClass(dotsWork[i], dotsWork[count]);
item.addEventListener('click', function() {
count = i;
// multiply the slide size by the number of the dots, and get the number by which you need to move the slider
slidWidth = sliderItem[0].clientWidth * i;
slider.style.transform = `translateX(-${slidWidth}px)`;
for(let j = 0; j < dotsWork.length; j++) {
dotsClass(dotsWork[j], dotsWork[count]);
}
if(set.dots && set.numberSlid) {
numberSliderWork(count);
}
if(set.line) {
sliderExecutionLineWork(count);
}
});
});
};
dotsFunk();
}
//===== count slider
if(set.numberSlid) {
numberSlider = function(item) {
const countContainer = document.createElement('div'),
sliderNumber = document.createElement('span'),
slash = document.createElement('span'),
allSliderNumber = document.createElement('span');
casClient = document.createElement('p');
sliderNumber.innerHTML = item + 1;
casClient.innerHTML = 'Cas client N°';
slash.innerHTML = '/';
allSliderNumber.innerHTML = sliderItem.length;
countContainer.classList.add('count-slides');
countContainer.append(casClient, sliderNumber, slash, allSliderNumber);
sliderContainer.append(countContainer);
};
numberSlider(0);
numberSliderWork = function(item) {
const sliderNumberNow = sliderContainer.querySelector('.count-slides span');
sliderNumberNow.innerHTML = item + 1;
if(set.line) {
sliderExecutionLineWork(item);
}
};
}
}
slider({
name: ".video_users",
numberSlid: true
});<!DOCTYPE html>
<html lang="fr">
<head>
<title>Example of a page without the slider</title>
</head>
<body class="error_404">
<h1>Example of a page without the slider</h1>
<script src="media/js/faveod.js" async></script>
</body>
</html>
>Solution :
Just return if the element isn’t present if you don’t want it to show an error.
const sliderContainer = document.querySelector(set.name);
if (!sliderContainer) return;
const slider = sliderContainer.querySelector('.slider'),
sliderItem = slider.querySelectorAll('.slider__item'),
sliderArrows = sliderContainer.querySelectorAll('.arrows__item');
If you want it to only execute on certain pages, then just add:
if (location.pathname !== '/the/page/with/slider') return;
to the beginning of the function