Regular Expressions: Remove Whitespace from Start and End

Regular Expressions: Remove Whitespace from Start and End
Sometimes whitespace characters around strings are not wanted but are there. Typical processing of strings is to remove the whitespace at the start and end of it.


Write a regex and use the appropriate string methods to remove whitespace at the beginning and end of strings.

Note
The .trim() method would work here, but you'll need to complete this challenge using regular expressions.

RegEx: Positive and Negative Lookahead

Regular Expressions: Positive and Negative Lookahead
Lookaheads are patterns that tell JavaScript to look-ahead in your string to check for patterns further along. This can be useful when you want to search for multiple patterns over the same string.

There are two kinds of lookaheads: positive lookahead and negative lookahead.

A positive lookahead will look to make sure the element in the search pattern is there, but won't actually match it. A positive lookahead is used as (?=...) where the ... is the required part that is not matched.

On the other hand, a negative lookahead will look to make sure the element in the search pattern is not there. A negative lookahead is used as (?!...) where the ... is the pattern that you do not want to be there. The rest of the pattern is returned if the negative lookahead part is not present.

Lookaheads are a bit confusing but some examples will help.

let quit = "qu";
let noquit = "qt";
let quRegex= /q(?=u)/;
let qRegex = /q(?!u)/;
quit.match(quRegex); // Returns ["q"]
noquit.match(qRegex); // Returns ["q"]
A more practical use of lookaheads is to check two or more patterns in one string. Here is a (naively) simple password checker that looks for between 3 and 6 characters and at least one number:

let password = "abc123";
let checkPass = /(?=\w{3,6})(?=\D*\d)/;
checkPass.test(password); // Returns true

Use lookaheads in the pwRegex to match passwords that are greater than 5 characters long and have two consecutive digits.

Regular Expressions: Restrict Possible Usernames

Regular Expressions: Restrict Possible Usernames
Usernames are used everywhere on the internet. They are what give users a unique identity on their favorite sites.

You need to check all the usernames in a database. Here are some simple rules that users have to follow when creating their username.

1) The only numbers in the username have to be at the end. There can be zero or more of them at the end.

2) Username letters can be lowercase and uppercase.

3) Usernames have to be at least two characters long. A two-letter username can only use alphabet letter characters.


Change the regex userCheck to fit the constraints listed above.

Regular Expressions: Find One or More Criminals in a Hunt

Regular Expressions: Find One or More Criminals in a Hunt
Time to pause and test your new regex writing skills. A group of criminals escaped from jail and ran away, but you don't know how many. However, you do know that they stay close together when they are around other people. You are responsible for finding all of the criminals at once.

Here's an example to review how to do this:

The regex /z+/ matches the letter z when it appears one or more times in a row. It would find matches in all of the following strings:

"z"
"zzzzzz"
"ABCzzzz"
"zzzzABC"
"abczzzzzzzzzzzzzzzzzzzzzabc"
But it does not find matches in the following strings since there are no letter z characters:

""
"ABC"
"abcabc"

Write a greedy regex that finds one or more criminals within a group of other people. A criminal is represented by the capital letter C.

Regular Expressions: Match Single Characters Not Specified

Regular Expressions: Match Single Characters Not Specified
So far, you have created a set of characters that you want to match, but you could also create a set of characters that you do not want to match. These types of character sets are called negated character sets.

To create a negated character set, you place a caret character (^) after the opening bracket and before the characters you do not want to match.

For example, /[^aeiou]/gi matches all characters that are not a vowel. Note that characters like ., !, [, @, / and white space are matched - the negated vowel character set only excludes the vowel characters.


Create a single regex that matches all characters that are not a number or a vowel. Remember to include the appropriate flags in the regex.

Regular Expressions: Match Numbers and Letters of the Alphabet

Regular Expressions: Match Numbers and Letters of the Alphabet
Using the hyphen (-) to match a range of characters is not limited to letters. It also works to match a range of numbers.

For example, /[0-5]/ matches any number between 0 and 5, including the 0 and 5.

Also, it is possible to combine a range of letters and numbers in a single character set.

let jennyStr = "Jenny8675309";
let myRegex = /[a-z0-9]/ig;
// matches all letters and numbers in jennyStr
jennyStr.match(myRegex);

Create a single regex that matches a range of letters between h and s, and a range of numbers between 2 and 6. Remember to include the appropriate flags in the regex.

Regular Expressions: Match Letters of the Alphabet

Regular Expressions: Match Letters of the Alphabet
You saw how you can use character sets to specify a group of characters to match, but that's a lot of typing when you need to match a large range of characters (for example, every letter in the alphabet). Fortunately, there is a built-in feature that makes this short and simple.

Inside a character set, you can define a range of characters to match using a hyphen character: -.

For example, to match lowercase letters a through e you would use [a-e].

let catStr = "cat";
let batStr = "bat";
let matStr = "mat";
let bgRegex = /[a-e]at/;
catStr.match(bgRegex); // Returns ["cat"]
batStr.match(bgRegex); // Returns ["bat"]
matStr.match(bgRegex); // Returns null

Match all the letters in the string quoteSample.

Note
Be sure to match both upper- and lowercase letters.

Regular Expressions: Match Single Character with Multiple Possibilities

Regular Expressions: Match Single Character with Multiple Possibilities
You learned how to match literal patterns (/literal/) and wildcard character (/./). Those are the extremes of regular expressions, where one finds exact matches and the other matches everything. There are options that are a balance between the two extremes.

You can search for a literal pattern with some flexibility with character classes. Character classes allow you to define a group of characters you wish to match by placing them inside square ([ and ]) brackets.

For example, you want to match "bag", "big", and "bug" but not "bog". You can create the regex /b[aiu]g/ to do this. The [aiu] is the character class that will only match the characters "a", "i", or "u".

let bigStr = "big";
let bagStr = "bag";
let bugStr = "bug";
let bogStr = "bog";
let bgRegex = /b[aiu]g/;
bigStr.match(bgRegex); // Returns ["big"]
bagStr.match(bgRegex); // Returns ["bag"]
bugStr.match(bgRegex); // Returns ["bug"]
bogStr.match(bgRegex); // Returns null

Use a character class with vowels (a, e, i, o, u) in your regex vowelRegex to find all the vowels in the string quoteSample.

Note
Be sure to match both upper- and lowercase vowels.

RegEx: Extract Matches

Regular Expressions: Extract Matches
So far, you have only been checking if a pattern exists or not within a string. You can also extract the actual matches you found with the .match() method.

To use the .match() method, apply the method on a string and pass in the regex inside the parentheses. Here's an example:

"Hello, World!".match(/Hello/);
// Returns ["Hello"]
let ourStr = "Regular expressions";
let ourRegex = /expressions/;
ourStr.match(ourRegex);
// Returns ["expressions"]

Apply the .match() method to extract the word coding.

Regular Expressions: Using the Test Method

Regular Expressions: Using the Test Method
Regular expressions are used in programming languages to match parts of strings. You create patterns to help you do that matching.

If you want to find the word "the" in the string "The dog chased the cat", you could use the following regular expression: /the/. Notice that quote marks are not required within the regular expression.

JavaScript has multiple ways to use regexes. One way to test a regex is using the .test() method. The .test() method takes the regex, applies it to a string (which is placed inside the parentheses), and returns true or false if your pattern finds something or not.

let testStr = "freeCodeCamp";
let testRegex = /Code/;
testRegex.test(testStr);
// Returns true

#100DAYSOFCODE D28 - Basic JavaScript: Escape Sequences in Strings

Quotes are not the only characters that can be escaped inside a string. There are two reasons to use escaping characters: First is to allow you to use characters you might not otherwise be able to type out, such as a backspace. Second is to allow you to represent multiple quotes in a string without JavaScript misinterpreting what you mean. We learned this in the previous challenge.

Code	Output
\'	single quote
\"	double quote
\\	backslash
\n	newline
\r	carriage return
\t	tab
\b	backspace
\f	form feed

Note that the backslash itself must be escaped in order to display as a backslash.

---

Assign the following three lines of text into the single variable myStrusing escape sequences.

FirstLine
    \SecondLine
ThirdLine

You will need to use escape sequences to insert special characters correctly. You will also need to follow the spacing as it looks above, with no spaces between escape sequences or words.

Here is the text with the escape sequences written out.

FirstLine newlinetabbackslash SecondLinenewline ThirdLine

freecodecamp: Title Case a Sentence

Goal: Return the provided string with the first letter of each word capitalized. Make sure the rest of the word is in lower case.

Solution: I used regular expression to select the first letterof each word and converting them to uppercase.