In JavaScript there are two ways to create regular expressions.

In the first way, one can write a pattern of letters, numbers or symbols enclosed in forward slash(/) characters, like so:

let regex1 = /xyz123/;

When using this first method of constructing regular expressions, certain special characters, like a question mark(?), asterisk/star(*), dollar sign($), vertical pipe symbol (|), period/dot (.), opening or closing parenthesis, and certain other special characters, need to have a back slash ( \ ) before their character in order be included in the pattern that the regular expression is searching for, as in the following cases:

let regex1question = /xyz123\?/;

let regex1pipe = /xyz123\|/;

let regex1money = /xyz123\$/;

In the second method of constructing regular expressions, one can use the RegExp constructor:

new RegExp()

With the RegExp constructor, one encloses the pattern of letters, numbers or symbols in quotation marks, like a string, within parentheses:

let regex2 = new RegExp("xyz123");

let regex2money = new RegExp("xyz123$")

A regular expression object in JavaScript has methods that can be used on it. For example, the method test returns a Boolean which indicates whether the string passed as an argument in the test method matches the pattern of the regular expression. For example:

console.log(/123xyz/.test("123xyz456"));

will return true since the pattern "123xyz" is contained in the string "123xyz456".

On the other hand the following:

console.log(/123xyz/.test("123zzz456"));

will return false, since the pattern "123xyz" is not contained in the string "123zzz456".

However, if we want to test whether or not a string contains any of the characters in a pattern, we can put the characters in regular expression between square brackets, as in the following:

console.log(/[123xyz]/.test("zzz"));

This will return true, since the string "zzz" does contain the character "z" from the pattern "123xyz".

We can also use certain shortcuts to indicate if we are searching for a certain type of character. For example,

\d indicates any character that is a digit between 0 and 9 (inclusive).

\w indicates any alphanumeric character

\W indicates any non-alphanumeric character

\D indicates any number that is not a digit

Further reading:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/RegExp