Improved Types

Summary: Improves the types for Easing and bezier to make them script.

Differential Revision: D10346234

fbshipit-source-id: e941110c62f7dcd17b0d022497cf29e0935db5a3

Libraries/Animated/src/Easing.js

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
@@ -175,10 +175,7 @@ class Easing {
    *
    * - http://tiny.cc/back_default (s = 1.70158, default)
    */
-  static back(s: number): (t: number) => number {
-    if (s === undefined) {
-      s = 1.70158;
-    }
+  static back(s: number = 1.70158): (t: number) => number {
     return t => t * t * ((s + 1) * t - s);
   }
 
@@ -193,17 +190,17 @@ class Easing {
     }
 
     if (t < 2 / 2.75) {
-      t -= 1.5 / 2.75;
-      return 7.5625 * t * t + 0.75;
+      const t2 = t - 1.5 / 2.75;
+      return 7.5625 * t2 * t2 + 0.75;
     }
 
     if (t < 2.5 / 2.75) {
-      t -= 2.25 / 2.75;
-      return 7.5625 * t * t + 0.9375;
+      const t2 = t - 2.25 / 2.75;
+      return 7.5625 * t2 * t2 + 0.9375;
     }
 
-    t -= 2.625 / 2.75;
-    return 7.5625 * t * t + 0.984375;
+    const t2 = t - 2.625 / 2.75;
+    return 7.5625 * t2 * t2 + 0.984375;
   }
 
   /**

Libraries/Animated/src/bezier.js

@@ -7,7 +7,7 @@
  * BezierEasing - use bezier curve for transition easing function
  * https://github.com/gre/bezier-easing
  *
- * @flow
+ * @flow strict
  * @format
  * @copyright 2014-2015 Gaëtan Renaudeau. MIT License.
  */
@@ -45,10 +45,12 @@ function getSlope(aT, aA1, aA2) {
   return 3.0 * A(aA1, aA2) * aT * aT + 2.0 * B(aA1, aA2) * aT + C(aA1);
 }
 
-function binarySubdivide(aX, aA, aB, mX1, mX2) {
+function binarySubdivide(aX, _aA, _aB, mX1, mX2) {
   let currentX,
     currentT,
-    i = 0;
+    i = 0,
+    aA = _aA,
+    aB = _aB;
   do {
     currentT = aA + (aB - aA) / 2.0;
     currentX = calcBezier(currentT, mX1, mX2) - aX;
@@ -64,7 +66,8 @@ function binarySubdivide(aX, aA, aB, mX1, mX2) {
   return currentT;
 }
 
-function newtonRaphsonIterate(aX, aGuessT, mX1, mX2) {
+function newtonRaphsonIterate(aX, _aGuessT, mX1, mX2) {
+  let aGuessT = _aGuessT;
   for (let i = 0; i < NEWTON_ITERATIONS; ++i) {
     const currentSlope = getSlope(aGuessT, mX1, mX2);
     if (currentSlope === 0.0) {