checkScroll()

in inflation-explorer/shared/js/scrollytellerProgress.js [39:110]
52 lines of code
11 McCabe index (conditional complexity)

    checkScroll() {
        if(this.on && this.lastScroll !== window.pageYOffset) {
            const bbox = this.scrollText.getBoundingClientRect();

            if(!supportsSticky) {
                if(bbox.top <= 0 && bbox.bottom >= window.innerHeight) {
                    this.scrollInner.classed("fixed-top", true);
                    this.scrollInner.classed("absolute-bottom", false);
                    this.scrollInner.classed("absolute-top", false);
                } else if(bbox.top <= 0) {
                    this.scrollInner.classed("fixed-top", false);
                    this.scrollInner.classed("absolute-bottom", true);
                    this.scrollInner.classed("absolute-top", false);
                } else {
                    this.scrollInner.classed("fixed-top", false);
                    this.scrollInner.classed("absolute-bottom", false);
                    this.scrollInner.classed("absolute-top", true);
                }
            }

            const scrollyStartPoint = window.innerHeight * this.triggerTop // point in window at which scrolly is triggered

            if(bbox.top < scrollyStartPoint && bbox.bottom > scrollyStartPoint) { 

                let indx = 0

                const neg = Math.floor(Math.abs(bbox.top - (window.innerHeight*(this.triggerTop))))

                indx = this.textBoxes.findIndex( (el, j,arr) => {

                    const soFar = arr.slice(0, j).map( el => el.getBoundingClientRect().height ).reduce(sum, 0)
                    return soFar > neg

                } ) - 1

                const i = indx < 0 ? this.textBoxes.length -1 : indx; // default to the last box if box indx is not found

                const overallP = (bbox.top - scrollyStartPoint)/bbox.height*(-1)

                this.onOverallProgress(overallP)

                const prevBox = this.textBoxes[i]   

                const abs = window.innerHeight*this.triggerTop - prevBox.getBoundingClientRect().top 
                const total = prevBox.getBoundingClientRect().height 
                const progressInBox = abs / total;  

                this.onGradualChange(progressInBox, i, abs, total)



                if(i !== this.lastI) {
                    this.lastI = i; 
                    this.doScrollAction(i);

                    if(this.transparentUntilActive) {
                        this.textBoxes.forEach((el, j) => {
                            if(j <= i) {
                                el.style.opacity = "1";
                            } else {
                                el.style.opacity = "0.25";
                            }
                        });
                    }
                }
            }
    
            this.lastScroll = window.pageYOffset;
        }
    
        window.requestAnimationFrame(this.checkScroll.bind(this));
    }