fix: fake behavior with special replacement patterns (#688)

src/fake.ts

@@ -46,32 +46,25 @@ export class Fake {
    * faker.fake('I flipped the coin an got: {{random.arrayElement(["heads", "tails"])}}') // 'I flipped the coin an got: tails'
    */
   fake(str: string): string {
-    // setup default response as empty string
-    let res = '';
-
     // if incoming str parameter is not provided, return error message
     if (typeof str !== 'string' || str.length === 0) {
       throw new Error('string parameter is required!');
     }
 
     // find first matching {{ and }}
-    const start = str.search('{{');
-    const end = str.search('}}');
+    const start = str.search(/{{[a-z]/);
+    const end = str.indexOf('}}', start);
 
     // if no {{ and }} is found, we are done
     if (start === -1 || end === -1) {
       return str;
     }
 
-    // console.log('attempting to parse', str);
-
     // extract method name from between the {{ }} that we found
     // for example: {{name.firstName}}
-    const token = str.substring(start + 2, end);
+    const token = str.substring(start + 2, end + 2);
     let method = token.replace('}}', '').replace('{{', '');
 
-    // console.log('method', method)
-
     // extract method parameters
     const regExp = /\(([^)]+)\)/;
     const matches = regExp.exec(method);
@@ -111,13 +104,14 @@ export class Fake {
 
     let result: string;
     if (typeof params === 'string' && params.length === 0) {
-      result = fn();
+      result = String(fn());
     } else {
-      result = fn(params);
+      result = String(fn(params));
     }
 
-    // replace the found tag with the returned fake value
-    res = str.replace('{{' + token + '}}', result);
+    // Replace the found tag with the returned fake value
+    // We cannot use string.replace here because the result might contain evaluated characters
+    const res = str.substring(0, start) + result + str.substring(end + 2);
 
     if (res === '') {
       return '';

test/fake.spec.ts

@@ -50,5 +50,39 @@ describe('fake', () => {
     it('should be able to return empty strings', () => {
       expect(faker.fake('{{helpers.repeatString}}')).toBe('');
     });
+
+    it('should be able to handle only {{ brackets', () => {
+      expect(faker.fake('{{hello')).toBe('{{hello');
+      expect(faker.fake('hello{{')).toBe('hello{{');
+    });
+
+    it('should be able to handle only }} brackets', () => {
+      expect(faker.fake('hello}}')).toBe('hello}}');
+      expect(faker.fake('}}hello')).toBe('}}hello');
+    });
+
+    it('should be able to handle reverted brackets', () => {
+      expect(faker.fake('}}hello{{')).toBe('}}hello{{');
+    });
+
+    it('should be able to handle random }} brackets', () => {
+      expect(faker.fake('}}hello{{random.alpha}}')).toMatch(/^}}hello[a-z]$/);
+    });
+
+    it('should be able to handle connected brackets', () => {
+      expect(faker.fake('{{{random.alpha}}}')).toMatch(/^{[a-z]}$/);
+    });
+
+    it('should be able to handle empty brackets', () => {
+      expect(faker.fake('{{}}')).toBe('{{}}');
+    });
+
+    it('should be able to handle special replacement patterns', () => {
+      (faker.random as any).special = () => '$&';
+
+      expect(faker.fake('{{random.special}}')).toBe('$&');
+
+      delete (faker.random as any).special;
+    });
   });
 });