Used getBoundingClientRect function instead of getOffsetSum

Author: hsnaydd

src/moveTo.js

@@ -25,28 +25,6 @@ const MoveTo = (() => {
     return -c * (t * t * t * t - 1) + b;
   }
 
-  /**
-   * Returns html element's top and left offset
-   * @param  {HTMLElement} elem - Element
-   * @return {object} Element top and left offset
-   */
-  function getOffsetSum(elem) {
-    if(typeof elem.getBoundingClientRect == 'function') {
-      return elem.getBoundingClientRect();
-    } else {
-      let top = 0;
-      let left = 0;
-      while (elem) {
-        top += elem.offsetTop;
-        left += elem.offsetLeft;
-        elem = elem.offsetParent;
-      }
-      return {
-        top, left,
-      };
-    }
-  }
-
   /**
    * Merge two object
    *
@@ -132,12 +110,11 @@ const MoveTo = (() => {
 
     options = mergeObject(this.options, options);
 
-    let to = typeof target === 'number' ? target : getOffsetSum(target).top;
+    let distance = typeof target === 'number' ? target : target.getBoundingClientRect().top;
     const from = window.pageYOffset;
-    to -= options.tolerance;
-    const change = to - from;
     let startTime = null;
     let lastPageYOffset;
+    distance -= options.tolerance;
 
     // rAF loop
     const loop = (currentTime) => {
@@ -154,24 +131,24 @@ const MoveTo = (() => {
 
       if (lastPageYOffset) {
         if (
-          (change > 0 && lastPageYOffset > currentPageYOffset) ||
-          (change < 0 && lastPageYOffset < currentPageYOffset)
+          (distance > 0 && lastPageYOffset > currentPageYOffset) ||
+          (distance < 0 && lastPageYOffset < currentPageYOffset)
         ) {
           return options.callback(target);
         }
       }
       lastPageYOffset = currentPageYOffset;
 
       const val = this.easeFunctions[options.easing](
-        timeElapsed, from, change, options.duration
+        timeElapsed, from, distance, options.duration
       );
 
       window.scroll(0, val);
 
       if (timeElapsed < options.duration) {
         window.requestAnimationFrame(loop);
       } else {
-        window.scroll(0, to);
+        window.scroll(0, distance + from);
         options.callback(target);
       }
     };

tests/moveTo-spec.js

@@ -21,6 +21,9 @@ function createMockDomElement(options) {
     },
     removeEventListener: function(event, cb) {
       delete this._listeners[event];
+    },
+    getBoundingClientRect: function() {
+      return {top: options.offsetTop || 0};
     }
   };
 }