feat(size): allow to specify string length of random values

README.md

@@ -47,6 +47,12 @@ const user = { email: randEmail(), name: randFullName() };
 const emails = randEmail({ length: 10 });
 ```
 
+You can specify the length of elements you want to generate. Below is an example of generating 10 emails with length equal or smaller than 20 characters.
+
+```ts
+const emails = randEmail({ length: 10, maxCharCount: 20 });
+```
+
 ### Setting a Randomness Seed
 
 You can set your own seed if you want consistent results:

packages/falso/src/lib/core/core.ts

@@ -1,8 +1,10 @@
 import { random } from '../random';
+import { isString } from '../utils/validators.utils';
 
 export interface FakeOptions {
   length?: number;
   locale?: any | string[];
+  maxCharCount?: number;
 }
 
 export type markRequired<Type, Key extends keyof Type> = Type & {
@@ -21,9 +23,16 @@ export function fake<T, Options extends FakeOptions>(
   data: Readonly<T[]> | FactoryFunction<T>,
   options?: Options
 ): Return<T, Options> {
-  const dataSource = Array.isArray(data)
-    ? () => randElement(data)
-    : (data as FactoryFunction<T>);
+  let dataSource = data as FactoryFunction<T>;
+  if (Array.isArray(data)) {
+    let resolvedData = data;
+    if (options?.maxCharCount && isString(data[0])) {
+      resolvedData = data.filter(
+        (item) => item.length <= options.maxCharCount!
+      );
+    }
+    dataSource = () => randElement(resolvedData);
+  }
 
   if (options?.length === undefined) {
     return dataSource(0) as any;

packages/falso/src/lib/utils/validators.utils.ts

@@ -0,0 +1,3 @@
+export function isString(value: any): value is string {
+  return typeof value === 'string';
+}

packages/falso/src/tests/max-char-count.spec.ts

@@ -0,0 +1,25 @@
+import { randAccount } from '../lib/account';
+import { randMovie } from '../lib/movie';
+
+describe('maxCharCount', () => {
+  it('should return 10 random movies with name length equal or smaller than 8', () => {
+    const result = randMovie({ length: 20, maxCharCount: 8 });
+
+    expect(result).toHaveLength(20);
+    result.forEach((movie) => expect(movie.length).toBeLessThanOrEqual(8));
+  });
+
+  it('should return 10 random movies with name length equal or smaller than 1', () => {
+    const result = randMovie({ length: 50, maxCharCount: 1 });
+
+    expect(result).toHaveLength(50);
+    result.forEach((movie) => expect(movie.length).toBeLessThanOrEqual(1));
+  });
+
+  it('should return 10 random movies with name length equal or smaller than 20', () => {
+    const result = randAccount({ length: 20, maxCharCount: 20 });
+
+    expect(result).toHaveLength(20);
+    result.forEach((account) => expect(account.length).toBeLessThanOrEqual(20));
+  });
+});

packages/falso/src/tests/movie.spec.ts

@@ -4,4 +4,8 @@ describe('movie', () => {
   it('should return a random movie (type string)', () => {
     expect(typeof randMovie()).toEqual('string');
   });
+
+  it('should return 10 random movies', () => {
+    expect(randMovie({ length: 10 })).toHaveLength(10);
+  });
 });