refactor!: Make "getResult" return null (#746)

src/Indicator.test.ts

@@ -25,6 +25,19 @@ describe('Indicator', () => {
     });
   });
 
+  describe('getResult', () => {
+    it('returns the result if an indicator is stable', () => {
+      const itc = new IndicatorTestClass();
+      itc.add(1);
+      expect(itc.getResult()?.toFixed()).toBe('1');
+    });
+
+    it("returns null if an indicator isn't stable", () => {
+      const itc = new IndicatorTestClass();
+      expect(itc.getResult()).toBe(null);
+    });
+  });
+
   describe('getResultOrThrow', () => {
     it('throws an error when there is not enough input data', () => {
       const itc = new IndicatorTestClass();

src/Indicator.ts

@@ -2,18 +2,29 @@ import type {BigSource} from 'big.js';
 import {NotEnoughDataError} from './error/NotEnoughDataError.js';
 import {getLastFromForEach} from './util/getLastFromForEach.js';
 
+type Nullable<Result> = Result | null;
+
 interface Indicator<Result = Big, Input = BigSource> {
-  getResultOrThrow(): Result;
   isStable: boolean;
-  add(input: Input): Result | null;
-  replace(input: Input): Result | null;
-  update(input: Input, replace: boolean): Result | null;
-  updates(input: Input[], replace: boolean): Result | null;
+  add(input: Input): Nullable<Result>;
+  getResult(): Nullable<Result>;
+  getResultOrThrow(): Result;
+  replace(input: Input): Nullable<Result>;
+  update(input: Input, replace: boolean): Nullable<Result>;
+  updates(input: Input[], replace: boolean): Nullable<Result>;
 }
 
 export abstract class TechnicalIndicator<Result, Input> implements Indicator<Result, Input> {
   protected result: Result | undefined;
 
+  getResult() {
+    try {
+      return this.getResultOrThrow();
+    } catch {
+      return null;
+    }
+  }
+
   getResultOrThrow() {
     if (this.result === undefined) {
       throw new NotEnoughDataError();