laipower/wp-content/themes/generatepress/assets/js/back-to-top.js

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JavaScript
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( function() {
'use strict';
// Feature Test
if ( 'querySelector' in document && 'addEventListener' in window ) {
var goTopBtn = document.querySelector( '.generate-back-to-top' );
var trackScroll = function() {
var scrolled = window.pageYOffset;
var coords = goTopBtn.getAttribute( 'data-start-scroll' );
if ( scrolled > coords ) {
goTopBtn.style.opacity = '1';
goTopBtn.style.visibility = 'visible';
}
if ( scrolled < coords ) {
goTopBtn.style.opacity = '0';
goTopBtn.style.visibility = 'hidden';
}
};
// Function to animate the scroll
var smoothScroll = function( anchor, duration ) {
// Calculate how far and how fast to scroll
var startLocation = window.pageYOffset;
var endLocation = document.body.offsetTop;
var distance = endLocation - startLocation;
var increments = distance / ( duration / 16 );
var stopAnimation;
// Scroll the page by an increment, and check if it's time to stop
var animateScroll = function() {
window.scrollBy( 0, increments );
stopAnimation();
};
// Stop animation when you reach the anchor OR the top of the page
stopAnimation = function() {
var travelled = window.pageYOffset;
if ( travelled <= ( endLocation || 0 ) ) {
clearInterval( runAnimation );
document.activeElement.blur();
}
};
// Loop the animation function
var runAnimation = setInterval( animateScroll, 16 );
};
if ( goTopBtn ) {
// Show the button when scrolling down.
window.addEventListener( 'scroll', trackScroll );
// Scroll back to top when clicked.
goTopBtn.addEventListener( 'click', function( e ) {
e.preventDefault();
if ( generatepressBackToTop.smooth ) {
smoothScroll( document.body, goTopBtn.getAttribute( 'data-scroll-speed' ) || 400 );
} else {
window.scrollTo( 0, 0 );
}
}, false );
}
}
}() );