Pull out assertDefined

packages/utils/src/assert.spec.ts

@@ -0,0 +1,52 @@
+import { assertDefined } from "./assert";
+
+describe("assert", () => {
+  describe("assertDefined", () => {
+    it("passes for simple values", () => {
+      {
+        const value: number | undefined = 123;
+        assertDefined(value);
+        expect(value).toEqual(123);
+      }
+      {
+        const value: string | undefined = "abc";
+        assertDefined(value);
+        expect(value).toEqual("abc");
+      }
+    });
+
+    it("passes for falsy values", () => {
+      {
+        const value: number | undefined = 0;
+        assertDefined(value);
+        expect(value).toEqual(0);
+      }
+      {
+        const value: string | undefined = "";
+        assertDefined(value);
+        expect(value).toEqual("");
+      }
+      {
+        const value: null | undefined = null;
+        assertDefined(value);
+        expect(value).toEqual(null);
+      }
+    });
+
+    it("throws for undefined values", () => {
+      {
+        const value: number | undefined = undefined;
+        expect(() => assertDefined(value)).toThrowError("value is undefined");
+      }
+      {
+        let value: string | undefined;
+        expect(() => assertDefined(value)).toThrowError("value is undefined");
+      }
+    });
+
+    it("throws with custom message", () => {
+      const value: number | undefined = undefined;
+      expect(() => assertDefined(value, "Bug in the data source")).toThrowError("Bug in the data source");
+    });
+  });
+});

packages/utils/src/assert.ts

@@ -4,3 +4,9 @@ export function assert(condition: any, msg?: string): asserts condition {
     throw new Error(msg || "condition is not truthy");
   }
 }
+
+export function assertDefined<T>(value: T | undefined, msg?: string): asserts value is T {
+  if (value === undefined) {
+    throw new Error(msg || "value is undefined");
+  }
+}

packages/utils/src/index.ts

@@ -1,3 +1,3 @@
-export { assert } from "./assert";
+export { assert, assertDefined } from "./assert";
 export { sleep } from "./sleep";
 export { isNonNullObject, isUint8Array } from "./typechecks";