Flatten workspace (#120)

packages/utils/src/shared/state.ts

@@ -0,0 +1,46 @@
+/**
+ * Slightly modified version of React's shallowEqual, with optimizations for Arrays
+ * so we may treat them specifically as unequal if they are not a) both arrays
+ * or b) don't contain the same (shallowly compared) elements.
+ */
+export function shallowEqual(objA: any, objB: any): boolean {
+  // Using Object.is as a first pass, as it covers a lot of the "simple" cases that are
+  // more complex than strict equality and is a built-in. For discussion, see, e.g.:
+  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is#description
+  if (Object.is(objA, objB)) {
+    return true;
+  }
+
+  // Since we've done an Object.is() check immediately above, we can safely assume non-objects (or null-valued objects)
+  // are not equal, so can early bail for those as well.
+  if (typeof objA !== 'object' || objA === null || typeof objB !== 'object' || objB === null) {
+    return false;
+  }
+
+  if (Array.isArray(objA)) {
+    // Early "cheap" array compares
+    if (!Array.isArray(objB) || objA.length !== objB.length) return false;
+    // Shallow compare for arrays
+    return objA.every((vVal, i) => objB[i] === vVal);
+  }
+
+  const keysA = Object.keys(objA);
+  const keysB = Object.keys(objB);
+
+  if (keysA.length !== keysB.length) {
+    return false;
+  }
+
+  // Test for A's keys different from B.
+  for (let i = 0; i < keysA.length; i++) {
+    // NOTE: Since we've already guaranteed the keys list lengths are the same, we can safely cast to string here (CJP)
+    if (
+      !globalThis.hasOwnProperty.call(objB, keysA[i] as string)
+      || !Object.is(objA[keysA[i] as string], objB[keysA[i] as string])
+    ) {
+      return false;
+    }
+  }
+
+  return true;
+}