Extracted custom easing name into constant

src/scrollToTarget.ts

 import * as Velocity from 'velocity-animate';
 import {HashTarget} from './HashTarget';
+import {EASE_IN_SKIP_OUT_EASING} from './setupVelocity';
 
 export function scrollToTarget(hashTarget: HashTarget): void
 {
 	Velocity.animate(hashTarget.getElement(), 'scroll', {
 		duration: 1200, // todo: different depending on offset from page top?
-		easing: 'ease-in-skip-out',
+		easing: EASE_IN_SKIP_OUT_EASING,
 		complete: () => window.location.hash = hashTarget.getHash(),
 	});
 }

src/setupVelocity.d.ts

 import * as Velocity from 'velocity-animate';
 
 declare const setupVelocity: (velocity: typeof Velocity) => void;
+export declare const EASE_IN_SKIP_OUT_EASING: string;
 export default setupVelocity;

src/setupVelocity.js

+export const EASE_IN_SKIP_OUT_EASING = 'ease-in-skip-out';
+
 // e.g. (5, 5, 10, 500, 1000) => 500
 // e.g. (5, 0, 10, 500, 1000) => 750
 const mapIntervalLinear = (number, originalFrom, originalTo, newFrom, newTo) => {
@@ -67,7 +69,7 @@ const computeHowMuchToSkip = (tweenDelta) => {
 };
 
 const setupVelocity = (velocity) => {
-	velocity.Easings['ease-in-skip-out'] = composeEasing(
+	velocity.Easings[EASE_IN_SKIP_OUT_EASING] = composeEasing(
 		(time, opts, tweenDelta) => mapIntervalLinear(
 			velocity.Easings['ease-in'](time, opts, tweenDelta),
 			0, 1, // from interval