Include require props helpers

Author: tristanmenzel

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@makerx/node-common",
-  "version": "1.1.0",
+  "version": "1.2.0",
   "private": false,
   "description": "A set of MakerX core NodeJS types and utilities",
   "author": "MakerX",

src/type-helpers/index.ts

@@ -0,0 +1 @@
+export * from './require-props'

src/type-helpers/require-props.ts

@@ -0,0 +1,50 @@
+/**
+ * Invariant assertion that the given object has the specified properties, and that they are not null or undefined.
+ *
+ * @param obj The object to check
+ * @param props The properties to check
+ *
+ * Usage:
+ * ```
+ * const obj: { maybeProp?: string } = { maybeProp: 'hello' }
+ *
+ * // Optional chaining required
+ * console.log(obj.maybeProp?.toLowerCase())
+ *
+ * requireProps(obj, 'maybeProp')
+ *
+ * // Optional chaining not required as we have asserted it is not null or undefined
+ * console.log(obj.maybeProp.toLowerCase())
+ * ```
+ */
+export function requireProps<T, TProps extends keyof T & string>(obj: T, ...props: TProps[]): asserts obj is RequireSomeProps<T, TProps> {
+  for (const prop of props) {
+    if (obj[prop] === undefined || obj[prop] === null) throw new Error(`Missing mandatory field ${prop}`)
+  }
+}
+
+/**
+ * Returns a filter function that: returns true if the given object has the specified properties, and they are not null or undefined.
+ * @param props The properties to check
+ *
+ * Usage:
+ * ```
+ * const objects: Array<{ maybeProp?: string }> = [{ maybeProp: 'hello' }, {}, {maybeProp: 'foo'}]
+ *
+ * // res1 type is Array<string | undefined> because there is no type assertion
+ * const res1 = objects.filter(x => x.maybeProp != undefined).map(x => x.maybeProp)
+ *
+ * // res2 type is Array<string> due to type assertion that required props will not be null or undefined
+ * const res2 = objects.filter(hasRequiredProps('maybeProp')).map(x => x.maybeProp)
+ * ```
+ */
+export const hasRequiredProps =
+  <T, TProps extends keyof T & string>(...props: TProps[]) =>
+  (obj: T): obj is RequireSomeProps<T, TProps> => {
+    requireProps(obj, ...props)
+    return true
+  }
+
+export type RequireSomeProps<T, TProps extends keyof T> = {
+  [key in TProps]-?: Exclude<T[key], null | undefined>
+} & T