As I continue my learning through algorithms, I start to recognize how some solutions are better for certain problems. Recently I was working my way through and came across this problem.

When I first read it, I thought this should be easy enough. Since there are several different test cases, I would have to pass in an argument to the function. I began to think okay but how do I even split up the numbers to insert parentheses and dashes? I gave myself about 10 mins before I gave up because I really had no idea. I went to Stack Overflow, a newbie developers best friend(at least mine anyway), and found a solution and it worked perfectly but I wanted to know why it worked. The solution had syntaxes that I don’t recall seeing before so I set out understand them.

Regular Expressions:

In Javascript, are patterns used to match character combinations in strings, they are also objects. These patterns are used with the exec() and test() methods of RegExp, and with the match(), matchAll(), replace(), replaceAll(), search(), and split() methods of String. I realized when it comes to string, using RegEx is method that can be very efficient when it comes to strings. How you put these expressions together determines your result.


The forward slash defines expressions, the characters between the slashes is what’s being searched.

Flags —

RegEx has several flag options that allow for functionality such a global search which is defined as g , it finds all the specified characters anywhere in the string. Case insensitive - i for case sensitive search, such as a capital letter. multi-line search - m , a boolean and is true if the "m" flag was used; otherwise false and a few others.

Plus sign + —

This expression matches one of more of the character preceding it, it matches as many of that character that is found.

? —

This expression will match one or more of each character that includes the preceding character.

The asterisk * —

This expression is a combination of + and ? , matches 0 or more.

The period /./ —

This expression matches any string that includes characters.

What if you want match all the periods? Using the backslash character allows you to search for all the periods

w —

Matches all alphabet characters.

d —

Matches any digit character 0–9.

s —

Matches any whitespace character; spaces,tabs & line breaks.

{} —

Allows you to specify the amount of characters you’d like to find.

Returns strings that are at least 5 characters long.

[] —

Matches any character within brackets.

finds any string that begins with f or c and ends with ‘at’
finds any string from a to z that ends ‘at’, adding ‘A-Z’ directly next to ‘a-z’ will find the case sensitive strings.

() —

Allows for grouping.

^ —

Matches the beginning of a line of the whole statement.

Adding the ‘m’ flag matches it for every line.

$ —

Matches the end of the string or line if ‘m’ flag is enabled.

There’s much more regular expressions but I’m only touching on the ones that I used to solve the problem above.

The replace() method 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. The match() method retrieves the result of matching a string against a regular expression.

more than 7 numbers given.

At first I thought Regex was scary like I thought about everything else when it comes to programming but once I took the time to really understand, I can see how it’s an efficient solution depending on the problem. I hope this was helpful to someone, as always happy coding !!

Links used in this blog:

The sassy developer