Axis-Aligned Bounding Box Intersection

AABB.js

// Class definition
function Rect() {
    this.x = this.y = 0;
    this.w = this.h = 1;
}

// Given two Axis-Aligned Bounding Boxes, check if any part of one contains any part of the other
function AABBIntersection(rectA, rectB) {
    // Local copies of rects so we can modify them
    let a = Object.assign({}, rectA), b = Object.assign({}, rectB);
    
    // If the width or height is negative for either bounding box, flip it
    if (a.w < 0) a.x -= a.w *= -1;
    if (a.h < 0) a.y -= a.h *= -1;
    if (b.w < 0) b.x -= b.w *= -1;
    if (b.h < 0) b.y -= b.h *= -1;
    
    // Now that the widths and heights are positive, check for sides which overlap or envelope the other rect
    return a.x < b.x + b.w && a.x + a.w >= b.x
        && a.y < b.y + b.h && a.y + a.h >= b.y;
}