Regular Expressions, references

• regular-expressions.info

• regex101.com

• YouTube: Best of Fluent 2012: /Reg(exp){2}lained/: Demystifying Regular Expressions

• MDN: Regular expressions

• RegExp() most popular instance methods:

  • rx.exec(str) - executes a search for a match in a specified string. Returns a result array, or null. Example with named capture groups.

  • rx.test(str) - executes a search for a match between a regular expression and a specified string. Returns true or false .

• String() most popular instance methods:

  • str.match(rx) - retrieves the result of matching a string against a regular expression.

    • const res = str.match(/rx/) - returns an array like object where res[0] contains the matched string.

    • const res = str.match(/rx/g) - returns an array/iterator of the matches - interchangeable of some simple usages of str.matchAll(rx) and rx.exec(str).

  • str.matchAll(rx) - returns an iterator of all results matching a string against a regular expression, including capturing groups - interchangeable of str.matchAll(rx).

  • str.replace(rx, 'replacement') - returns a new string with some or all matches of a pattern replaced by a replacement. The pattern can be a string or a RegExp, and the replacement can be a string or a function to be called for each match. If pattern is a string, only the first occurrence will be replaced. With RexExp and the global /g flag (switch) it can be used of interchangeable of str.replaceAll(rx)

  • str.replaceAll(rx, 'replacement') - returns a new string with all matches of a pattern replaced by a replacement. The pattern can be a string or a RegExp, and the replacement can be a string or a function to be called for each match.

  • str.search(rx) executes a search for a match between a regular expression and this String object. Returns the index of the first match between the regular expression and the given string, or -1 if no match was found.

    If you only want to know if it exists, use the similar test() method on the RegExp prototype, which returns a boolean and it is faster.

  • str.split(separator, limit) - divides a String into an ordered list of substrings, puts these substrings into an array, and returns the array. The division is done by searching for a pattern; where the pattern is provided as the first parameter in the method’s call.

    The separator can be a simple string or it can be a RegExp. If separator is a regular expression that contains capturing parentheses ( ), matched results are included in the array.

Exercises and the most interesting parts

Flag	Description	Corresponding property
d	Generate indices for substring matches.	RegExp.prototype.hasIndices
g	Global search.	RegExp.prototype.global
i	Case-insensitive search.	` RegExp.prototype.ignoreCase`
m	Multi-line search.	RegExp.prototype.multiline
s	Allows . to match newline characters.	RegExp.prototype.dotAll
u	“unicode”; treat a pattern as a sequence of unicode code points.	RegExp.prototype.unicode
y	Perform a “sticky” search that matches starting at the current position in the target string. See sticky.	RegExp.prototype.sticky

• Note that the flags are an integral part of a regular expression. They cannot be added or removed later.

• Creating regular expressions by the RegExp() constructor is preferable in the cases where we need to create a regexp dynamically from a string, for example based on the user’s input or some other variable.

    let rxVar = '\b\d+?\b';
    let rxVarFlags = 'ig';
    const rh = new RegExp(rxVar, rxVarFlags);
  

  In all other cases we should prefer the literal syntax - it’s shorter; it’s faster - because the regex object is created once…

    const rx = /\b\d+?\b/ig;
  

• Phone number exercise: exercise-1.validate-phone-number.html

• Exercises: homework/hw.2022.04.02

• Exercises: homework/hw.2022.04.03