add helper function docs

Author: zamronypj

assets/images/helping-hand.jpg

@@ -53,6 +53,7 @@ description: Documentation and developer's resources for Fano Framework, web app
 - [Sending email](/utilities/sending-email)
 - [Identifying client user-agent](/utilities/identifying-client-user-agent)
 - [Working with regular expression](/utilities/regular-expression)
+- [Helper functions](/utilities/helper-functions)
 - [Rate limiting request](/utilities/rate-limit)
 
 ## Database

documentation/index.md

@@ -7,8 +7,84 @@ description: Tutorial on how to use helper functions provided by Fano Framework
 
 ## About Helper function
 
-![Rate limiting](/assets/images/rate-limit.jpg){:class="image fit"}
+![Helper illustration](/assets/images/helping-hand.jpg){:class="image fit"}
 
-(Image by Ludovic Charlet [unsplash.com](https://unsplash.com/photos/CGWK6k2RduY)).
+Photo by [Austin Kehmeier](https://unsplash.com/@a_kehmeier?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText) on [Unsplash](https://unsplash.com/s/photos/helping-hand?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText)
 
+Fano Framework provides helper functions to simplify common tasks such as generate slug string, join string with delimiter or read file content.
 
+All helpers functions are declared in `fano.pas` unit.
+
+## Read file content to string
+
+`readFile()` reads file content and output is as string. It accepts one parameter file path of filename to load.
+
+```
+(*!------------------------------------------------
+ * read file to string
+ *-----------------------------------------------
+ * @param filepath file to load
+ * @returns contents of file as string
+ *-----------------------------------------------*)
+function readFile(const filepath : string) : string;
+```
+
+Please note, it may consume a lot of memories if file size is big.
+
+```
+var fileContent : string;
+...
+
+fileContent := readFile('/tmp/myfile');
+```
+
+## Join array of string as string
+
+`join()` function concatenates array of string as a single string with delimiter.
+
+```
+(*!------------------------------------------------
+ * join array of string with a delimiter
+ *-----------------------------------------------
+ * @param delimiter string to separate each
+ * @param values array of string to join
+ *-----------------------------------------------*)
+function join(const delimiter : string; const values : array of string) : string;
+```
+
+For example
+```
+var joinedStr : string;
+...
+
+//joinedStr = 'hello#good#people';
+joinedStr := join('#', ['hello', 'good', 'people']);
+```
+
+## Generate slug
+
+`slug()` function generates string consists of alpha numeric characters separated by dash characters and strips everything else.
+
+```
+(*!------------------------------------------------
+ * generate slug
+ *-----------------------------------------------
+ * @param originalStr input string
+ * @return slug
+ *-----------------------------------------------*)
+function slug(const originalStr : string) : string;
+```
+
+For example
+
+```
+var slugStr : string;
+...
+
+//slugStr = 'hello-good-people';
+slugStr := slug('hello    good  @##@$$@$people']);
+```
+
+## Explore more
+
+- [Regular expression](/utilities/regular-expression)

utilities/helper-functions/index.md

@@ -25,6 +25,10 @@ description: Tutorial on how to work with some utilities provided by Fano Framew
 
 - [Working with regular expression](/utilities/regular-expression)
 
+## Helper functions
+
+- [Helper functions](/utilities/helper-functions)
+
 ## Rate limiting request
 
 - [Rate limiting request](/utilities/rate-limit)