Add arrayContentStartsWith

CHANGELOG.md

@@ -29,6 +29,8 @@ and this project adheres to
   supported nested pubkeys for multisig. `SinglePubkey` is the old `PubKey` in
   which the `value` is a base64 encoded string. And `Secp256k1Pubkey` is a
   single secp256k1 pubkey.
+- @cosmjs/utils: The new `arrayContentStartsWith` works similar to
+  `arrayContentEquals` but only checks the start of an array.
 
 ### Changed
 

packages/utils/src/array.spec.ts

@@ -1,4 +1,4 @@
-import { arrayContentEquals } from "./arrays";
+import { arrayContentEquals, arrayContentStartsWith } from "./arrays";
 
 describe("array", () => {
   describe("arrayContentEquals", () => {
@@ -30,4 +30,32 @@ describe("array", () => {
       expect(arrayContentEquals([], new Uint8Array([]))).toEqual(true);
     });
   });
+
+  describe("arrayContentStartsWith", () => {
+    it("can compare number arrays", () => {
+      // same length
+      expect(arrayContentStartsWith([], [])).toEqual(true); // Same behaviour as "".startsWith("")
+      expect(arrayContentStartsWith([1, 2, 3], [1, 2, 3])).toEqual(true);
+      expect(arrayContentStartsWith([1, 2, 3], [1, 2, 8])).toEqual(false);
+      expect(arrayContentStartsWith([1, 2, 3], [0, 0, 0])).toEqual(false);
+
+      // a shorter than b
+      expect(arrayContentStartsWith([], [1, 2, 3])).toEqual(false);
+      expect(arrayContentStartsWith([1], [1, 2, 3])).toEqual(false);
+      expect(arrayContentStartsWith([1, 2], [1, 2, 3])).toEqual(false);
+
+      // a longer than b
+      expect(arrayContentStartsWith([1, 2, 3, 4, 5], [1, 2, 3, 4, 5])).toEqual(true);
+      expect(arrayContentStartsWith([1, 2, 3, 4, 5], [1, 2, 3, 4])).toEqual(true);
+      expect(arrayContentStartsWith([1, 2, 3, 4, 5], [1, 2, 3])).toEqual(true);
+      expect(arrayContentStartsWith([1, 2, 3, 4, 5], [1, 2])).toEqual(true);
+      expect(arrayContentStartsWith([1, 2, 3, 4, 5], [1])).toEqual(true);
+      expect(arrayContentStartsWith([1, 2, 3, 4, 5], [])).toEqual(true);
+      expect(arrayContentStartsWith([1, 2, 3, 4, 5], [1, 2, 3, 4, 0])).toEqual(false);
+      expect(arrayContentStartsWith([1, 2, 3, 4, 5], [1, 2, 3, 0])).toEqual(false);
+      expect(arrayContentStartsWith([1, 2, 3, 4, 5], [1, 2, 0])).toEqual(false);
+      expect(arrayContentStartsWith([1, 2, 3, 4, 5], [1, 0])).toEqual(false);
+      expect(arrayContentStartsWith([1, 2, 3, 4, 5], [0])).toEqual(false);
+    });
+  });
 });

packages/utils/src/arrays.ts

@@ -16,3 +16,22 @@ export function arrayContentEquals<T extends string | number | boolean>(
   }
   return true;
 }
+
+/**
+ * Checks if `a` starts with the contents of `b`.
+ *
+ * This requires equality of the element values, where element equality means `===` returning `true`.
+ *
+ * This allows you to compare the content of a Buffer, Uint8Array or number[], ignoring the specific type.
+ * As a consequence, this returns different results than Jasmine's `toEqual`, which ensures elements have the same type.
+ */
+export function arrayContentStartsWith<T extends string | number | boolean>(
+  a: ArrayLike<T>,
+  b: ArrayLike<T>,
+): boolean {
+  if (a.length < b.length) return false;
+  for (let i = 0; i < b.length; ++i) {
+    if (a[i] !== b[i]) return false;
+  }
+  return true;
+}

packages/utils/src/index.ts

@@ -1,4 +1,4 @@
-export { arrayContentEquals } from "./arrays";
+export { arrayContentEquals, arrayContentStartsWith } from "./arrays";
 export { assert, assertDefined, assertDefinedAndNotNull } from "./assert";
 export { sleep } from "./sleep";
 export { isNonNullObject, isUint8Array } from "./typechecks";