Add valueOrError.ts

packages/server/src/error/index.ts

@@ -1,2 +1,3 @@
 export * from './ErrorTransformer'
 export * from './TransformedError'
+export * from './valueOrError'

packages/server/src/error/valueOrError.test.ts

@@ -0,0 +1,34 @@
+import {valueOrError} from './'
+
+describe('valueOrError', () => {
+
+  it('throws a 404 error when value is undefined', () => {
+    expect(() => valueOrError(undefined)).toThrowError('Not Found')
+  })
+
+  it('throws a 404 error when value is null', () => {
+    expect(() => valueOrError(null)).toThrowError('Not Found')
+  })
+
+  it('returns the value when it is neither null, nor undefined', () => {
+    const obj = {}
+    expect(valueOrError(obj)).toBe(obj)
+    expect(valueOrError(0)).toBe(0)
+    expect(valueOrError(1)).toBe(1)
+    expect(valueOrError('')).toBe('')
+  })
+
+  it('returns a HTTP error with custom status code', () => {
+    expect(() => valueOrError(undefined, 400)).toThrowError('Bad Request')
+  })
+
+  it('removes undefined and null from function', () => {
+    function getValue(): number | undefined {
+      return 1
+    }
+    const obj1 = getValue()
+    const obj2: number = valueOrError(obj1)
+    expect(obj2).toEqual(1)
+  })
+
+})

packages/server/src/error/valueOrError.ts

@@ -0,0 +1,16 @@
+import createError from 'http-errors'
+
+/**
+ * Checks if the value is either null or undefined. If so, throws a Not Found
+ * HTTP error. Otherwise, returns the value. The parameter `statusCode` can be
+ * used to modify the error status code.
+ */
+export function valueOrError<T>(
+  value: T | undefined | null,
+  statusCode = 404,
+): T {
+  if (value === undefined || value === null) {
+    throw createError(statusCode)
+  }
+  return value
+}