Easing: revert to pre-ES2018 syntax.

lib/easing.js

@@ -11,53 +11,53 @@ const {
 
 const ease = {};
 ease.linear = n => n;
-ease.inQuad = n => n ** 2;
+ease.inQuad = n => n * n;
 ease.outQuad = n => n * (2 - n);
 ease.inOutQuad = n => {
   n *= 2;
   return n < 1 ?
     HALF * n * n :
     -HALF * (--n * (n - 2) - 1);
 };
-ease.inCube = n => n ** 3;
+ease.inCube = n => n * n * n;
 ease.outCube = n => --n * n * n + 1;
 ease.inOutCube = n => {
   n *= 2;
   return n < 1 ?
-    HALF * (n ** 3) :
+    HALF * (n * n * n) :
     HALF * ((n -= 2) * n * n + 2);
 };
 
-ease.inQuart = n => n ** 4;
-ease.outQuart = n => 1 - (--n * (n ** 3));
+ease.inQuart = n => n * n * n * n;
+ease.outQuart = n => 1 - (--n * (n * n * n));
 ease.inOutQuart = n => {
   n *= 2;
   return n < 1 ?
-    HALF * (n ** 4) :
-    -HALF * ((n -= 2) * (n ** 3) - 2);
+    HALF * (n * n * n * n) :
+    -HALF * ((n -= 2) * (n * n * n) - 2);
 };
 
-ease.inQuint = n => n ** 5;
-ease.outQuint = n => --n * (n ** 4) + 1;
+ease.inQuint = n => n * n * n * n * n;
+ease.outQuint = n => --n * (n * n * n * n) + 1;
 ease.inOutQuint = n => {
   n *= 2;
   return n < 1 ?
-    HALF * (n ** 5) :
-    HALF * ((n -= 2) * (n ** 4) + 2);
+    HALF * (n * n * n * n * n) :
+    HALF * ((n -= 2) * (n * n * n * n) + 2);
 };
 
 ease.inSine = n => 1 - cos(n * PI / 2);
 ease.outSine = n => sin(n * PI / 2);
 ease.inOutSine = n => HALF * (1 - cos(PI * n));
 
-ease.inExpo = n => 0 === n ? 0 : 1024 ** (n - 1);
-ease.outExpo = n => 1 === n ? n : 1 - 2 ** (-10 * n);
+ease.inExpo = n => 0 === n ? 0 : Math.pow(1024, n - 1);
+ease.outExpo = n => 1 === n ? n : 1 - Math.pow(2, -10 * n);
 ease.inOutExpo = n => {
   if (n === 0) { return 0; }
   if (n === 1) { return 1; }
   return (n *= 2) < 1 ?
-    HALF * (1024 ** (n - 1)) :
-    HALF * (-(2 ** (-10 * (n - 1))) + 2);
+    HALF * Math.pow(1024, n - 1) :
+    HALF * (-Math.pow(2, -10 * (n - 1)) + 2);
 };
 
 ease.inCirc = n => 1 - sqrt(1 - n * n);