Create more bot responses

• Change the code in "src/index.js"

• Understand "regular expression"

• Learn/Use "Natural Language Understanding (NLU)" APIs

Regular Expression (wiki)

• A regular expression, regex or regexp (sometimes called a rational expression) is a sequence of characters that define a search pattern. Usually such patterns are used by string searching algorithms for "find" or "find and replace" operations on strings, or for input validation. It is a technique developed in theoretical computer science and formal language theory.

Regular Expression Basics

.   : matches any single character except \n

*   : matches 0 or more instances of the preceding reg
exp

+   : matches 1 or more instances of the preceding reg exp

?   : matches 0 or 1 of the preceding regular expression

|   : matches the preceding or following reg exp

[ ] : defines a character class  (e.g. [a-zA-Z])

( ) : groups enclosed regular expression into a new reg exp

"…" : matches everything within the " " literally

Regular Expression Examples

* a natural number: e.g. 12345
==> [1-9][0-9]*

* a word: e.g. cat
==> [a-zA-Z]+

* a C/C++ variable: e.g. _name38
==> [_a-zA-Z][_0-9a-zA-Z]*

* a (possibly) signed integer: 12345 or -12345
==> [-+]?[1-9][0-9]*

* a floating point number: 1.2345
==> [0-9]*"."[0-9]+

More on Regular Expression

x|y	   x or y

x/y	   x, only if followed by y (y not removed from input)

x{m,n}     m to n occurrences of x

^x	   x, but only at beginning of line

x$	   x, but only at end of line

Meta Characters

• meta-characters (do not match themselves, because they are used in the preceding reg exps):
  ( ) [ ] { } < > + / , ^ * | . \ " $ ? - %

• to match a meta-character, prefix with \

• to match a backslash, tab or newline, use \\, \t, or \n

Regular Expression in Javascript

let re = /pattern/flags;

// or 

let re = new RegExp('pattern', 'flags');

Regular Expression Flags

Regular Expression Methods