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Update script.js #51

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170 changes: 67 additions & 103 deletions progress-nav/script.js
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Original file line number Diff line number Diff line change
@@ -1,128 +1,92 @@
window.onload = function() {

var toc = document.querySelector( '.toc' );
var tocPath = document.querySelector( '.toc-marker path' );
var tocItems;
const toc = document.querySelector('.toc');
const tocPath = document.querySelector('.toc-marker path');
let tocItems = [];

// Factor of screen size that the element must cross
// before it's considered visible
var TOP_MARGIN = 0.1,
BOTTOM_MARGIN = 0.2;
const TOP_MARGIN = 0.1,
BOTTOM_MARGIN = 0.2;

var pathLength;
let pathLength, lastPathStart, lastPathEnd;

var lastPathStart,
lastPathEnd;
window.addEventListener('resize', drawPath);
window.addEventListener('scroll', sync);

window.addEventListener( 'resize', drawPath, false );
window.addEventListener( 'scroll', sync, false );
drawPath();

drawPath();
function drawPath() {
tocItems = Array.from(toc.querySelectorAll('li')).map(item => {
const anchor = item.querySelector('a');
const target = document.getElementById(anchor.getAttribute('href').slice(1));

function drawPath() {
return { listItem: item, anchor, target };
}).filter(item => item.target);

tocItems = [].slice.call( toc.querySelectorAll( 'li' ) );
let path = [];
let pathIndent;

// Cache element references and measurements
tocItems = tocItems.map( function( item ) {
var anchor = item.querySelector( 'a' );
var target = document.getElementById( anchor.getAttribute( 'href' ).slice( 1 ) );
tocItems.forEach((item, i) => {
const x = item.anchor.offsetLeft - 5,
y = item.anchor.offsetTop,
height = item.anchor.offsetHeight;

return {
listItem: item,
anchor: anchor,
target: target
};
} );
if (i === 0) {
path.push(`M${x},${y}L${x},${y + height}`);
item.pathStart = 0;
} else {
if (pathIndent !== x) path.push(`L${pathIndent},${y}`);

// Remove missing targets
tocItems = tocItems.filter( function( item ) {
return !!item.target;
} );
path.push(`L${x},${y}`);

var path = [];
var pathIndent;
tocPath.setAttribute('d', path.join(' '));
item.pathStart = tocPath.getTotalLength() || 0;

tocItems.forEach( function( item, i ) {
path.push(`L${x},${y + height}`);
}

var x = item.anchor.offsetLeft - 5,
y = item.anchor.offsetTop,
height = item.anchor.offsetHeight;
pathIndent = x;

if( i === 0 ) {
path.push( 'M', x, y, 'L', x, y + height );
item.pathStart = 0;
}
else {
// Draw an additional line when there's a change in
// indent levels
if( pathIndent !== x ) path.push( 'L', pathIndent, y );
tocPath.setAttribute('d', path.join(' '));
item.pathEnd = tocPath.getTotalLength();
});

path.push( 'L', x, y );
pathLength = tocPath.getTotalLength();
sync();
}

// Set the current path so that we can measure it
tocPath.setAttribute( 'd', path.join( ' ' ) );
item.pathStart = tocPath.getTotalLength() || 0;
function sync() {
const windowHeight = window.innerHeight;

path.push( 'L', x, y + height );
}
let pathStart = pathLength,
pathEnd = 0,
visibleItems = 0;

pathIndent = x;
tocItems.forEach(item => {
const { top, bottom } = item.target.getBoundingClientRect();

tocPath.setAttribute( 'd', path.join( ' ' ) );
item.pathEnd = tocPath.getTotalLength();
if (bottom > windowHeight * TOP_MARGIN && top < windowHeight * (1 - BOTTOM_MARGIN)) {
pathStart = Math.min(item.pathStart, pathStart);
pathEnd = Math.max(item.pathEnd, pathEnd);
visibleItems++;

} );
item.listItem.classList.add('visible');
} else {
item.listItem.classList.remove('visible');
}
});

pathLength = tocPath.getTotalLength();
if (visibleItems > 0 && pathStart < pathEnd) {
if (pathStart !== lastPathStart || pathEnd !== lastPathEnd) {
tocPath.setAttribute('stroke-dashoffset', '1');
tocPath.setAttribute('stroke-dasharray', `1, ${pathStart}, ${pathEnd - pathStart}, ${pathLength}`);
tocPath.setAttribute('opacity', 1);
}
} else {
tocPath.setAttribute('opacity', 0);
}

sync();
lastPathStart = pathStart;
lastPathEnd = pathEnd;
}

}

function sync() {

var windowHeight = window.innerHeight;

var pathStart = pathLength,
pathEnd = 0;

var visibleItems = 0;

tocItems.forEach( function( item ) {

var targetBounds = item.target.getBoundingClientRect();

if( targetBounds.bottom > windowHeight * TOP_MARGIN && targetBounds.top < windowHeight * ( 1 - BOTTOM_MARGIN ) ) {
pathStart = Math.min( item.pathStart, pathStart );
pathEnd = Math.max( item.pathEnd, pathEnd );

visibleItems += 1;

item.listItem.classList.add( 'visible' );
}
else {
item.listItem.classList.remove( 'visible' );
}

} );

// Specify the visible path or hide the path altogether
// if there are no visible items
if( visibleItems > 0 && pathStart < pathEnd ) {
if( pathStart !== lastPathStart || pathEnd !== lastPathEnd ) {
tocPath.setAttribute( 'stroke-dashoffset', '1' );
tocPath.setAttribute( 'stroke-dasharray', '1, '+ pathStart +', '+ ( pathEnd - pathStart ) +', ' + pathLength );
tocPath.setAttribute( 'opacity', 1 );
}
}
else {
tocPath.setAttribute( 'opacity', 0 );
}

lastPathStart = pathStart;
lastPathEnd = pathEnd;

}

};
};