var smoothScroll = require("simplesmoothscroll");

// Passing in no params scrolls you to the top of the page
smoothScroll();

// Passing an element as a param scrolls you to that element
var myHeader = document.querySelector("h2");
smoothScroll(myHeader);

// You can also include an offset so there is some room between
// the top of the viewport and the element
smoothScroll(myHeader, {
  offset: 10
});

/**
 *  If you want to execute a function when the scroll finishes, you can
 *  pass in an onScrollFinished callback. A "cancelled" param is passed in
 *  as an arg in case the scroll was cancelled due to user interaction
 */
smoothScroll(myHeader, {
  offset: 10,
  onScrollFinished: function(cancelled) {
    // Your function
  }
});

/**
 * If you want your own easing function instead of the default trig-based
 * ease-in-out function, you can pass in a getEasingFunction parameter that
 * should return your custom easing function. "getEasingFunction" is passed in
 * the targetPosition (distance the target is from the viewport)
 * and the returned function will be passed a "stepCount" argument that
 * represents the number of frames since the scroll started.
 * The easing function should return a value between 0 and 1 where 0
 * will scroll to the initial position and 1 will scroll to the target.
 * Below is an example of using a custom linear scroll
 */
smoothScroll(myHeader, {
  getEasingFunction: function(targetPosition) {
    return function(stepCount) {
      return stepCount * 0.01;
    };
  }
});