What is it

Regular expressions (regexps) are patterns which describe the contents of a string. They're used for testing whether a string contains a given pattern, or extracting the portions that match.

Quantifier ?

The ? (quantifier) makes the preceding token in the regular expression optional

# matches both colour and color
colou?r 

# matches Nov and November
Nov(ember)?

Applying in JS

const method1 = new RegExp(/^---([\s\S]*?)---/).exec(someString);
const method2 = someString.match(/^---([\s\S]*?)---/);

// returns boolean of presence of text
const someRegex = new RegExp(/text/);
const method3 = someRegex.test("some really long text in a paragraph.");