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Regex Sets / Ranges

Regular Expressions: Regex Sets / Ranges

What is a set in JavaScript Regex?​

View Answer:
Interview Response: In JavaScript regular expressions, a set is defined by using square brackets [], which matches any one character enclosed in the brackets. For example, [abc] will match any one character being either 'a', 'b', or 'c'.

Code Example:

let str = "The quick brown fox jumps over the lazy dog.";

// Define a regex with a set
let regex = /[aeiou]/gi;

// Using the regex to find all vowels in the string
let result = str.match(regex);

console.log(result); // Outputs: ['e', 'u', 'i', 'o', 'o', 'u', 'o', 'e', 'e', 'a', 'o']

Can a set include a range in Regex?​

View Answer:
Interview Response: Yes, a set in Regex can include a range. You can specify a range of characters using a hyphen `-`. For instance, `[a-z]` matches any lowercase letter, `[A-Z]` matches any uppercase letter, and `[0-9]` matches any digit.

Code Example:

let str = "Hello, JS! 123";

// Define a regex with a set that includes a range
let regex = /[a-z0-9]/gi;

// Using the regex to find all alphanumeric characters in the string
let result = str.match(regex);

console.log(result); // ["H", "e", "l", "l", "o", "J", "S", "1", "2", "3"]

How do you specify multiple ranges in a Regex set?​

View Answer:
Interview Response: To specify multiple ranges in a Regex set, you simply include the multiple ranges within the square brackets. For example, `[a-zA-Z0-9]` will match any uppercase letter, lowercase letter, or digit.

Code Example:

let str = "Hello, JS! 123";

// Define a regex with a set that includes multiple ranges
let regex = /[a-zA-Z]/g;

// Using the regex to find all alphanumeric characters in the string
let result = str.match(regex);

console.log(result); 
// Outputs: ["H", "e", "l", "l", "o", "J", "S"]

What does a caret (^) inside a Regex set indicate?​

View Answer:
Interview Response: In a regular expression, a caret (^) at the start of a set (i.e., right after the opening square bracket) negates the set. This is often called a negated or complemented character set. It matches any character that is not in the set.

Code Example:

let str = "Hello, JS! 123";

// Define a regex with a set that includes a caret (^) to negate the set
let regex = /[^a-zA-Z0-9]/g;

// Using the regex to find all non-alphanumeric characters in the string
let result = str.match(regex);

console.log(result); 
// Outputs: [',', ' ', '!', ' ', ' ']

Can Regex sets contain special characters?​

View Answer:
Interview Response: Yes, It is crucial to keep in mind that when special characters are used in sets, they lose their intended function. This means that the special character will no longer function as it typically would, potentially causing errors or misunderstandings in the output. Therefore, it is important to be aware of the impact of special characters when utilizing them in sets.

How would you specify a regex set to match only lowercase vowels?​

View Answer:
Interview Response: To specify a regex set to match only lowercase vowels, you can use the following pattern'[aeiou]' which will match any lowercase vowel.

Code Example:

let str = "Hello my name is larry and I want you to know JavaScript!";

let regex = /[aeiou]/g;
let result = str.match(regex);

console.log(result);
// ["e", "o", "a", "e", "i", "a", "a", "a", "o", "u", "o", "o", "a", "a", "i"]

How do square brackets […] perform in regular expression sets?​

View Answer:
Interview Response: In regular expressions, square brackets [...] define a character set, matching any single character enclosed. For example, [abc] matches 'a', 'b', or 'c'. Ranges can be specified like [a-z] or [0-9].

Technical Response: Several characters or character classes inside square brackets […] mean to “search for any character among given”. For example, [eao] means any of the 3 characters: 'a', 'e', or 'o'. That is called a set in regex terminology. We use sets in a regular expressions along with recurring characters. We should note that although there are multiple characters in the set, they correspond to exactly one character in the match.

Code Example:

// find [t or m], and then "op"
console.log('Mop top'.match(/[tm]op/gi)); // "Mop", "top"

// Return null or no matches
// find "V", then [o or i], then "la"
console.log('Voila'.match(/V[oi]la/)); // null, no matches

Can you explain how range is set in a regular expression?​

View Answer:
Interview Response: In regular expressions, a range is set using square brackets and a hyphen. For example, [a-z] matches any lowercase letter, [A-Z] matches any uppercase letter, and [0-9] matches any digit.

Technical Response: In simple terms, a range in a regular expression is denoted or expressed inside of square brackets. A range may be from [a-z] or [1-100]. These settings can be set based on your needs. We can also use character classes inside […]. For example, if we would like to look for a wordy character \w or a hyphen -, then the set is [\w-]. Combining multiple classes is also possible, e.g. [\s\d] means “a space character or a digit”.

Code Example:

console.log('Exception 0xAF'.match(/x[0-9A-F][0-9A-F]/g)); // xAF

Is there a way to handle Han (Chinese) or Cyrillic in regexp ranges?​

View Answer:
Technical Response: Yes, Unicode range can be used in JavaScript regex. Unicode property escapes `\p{...}` can also be used to match characters that have certain general categories, scripts, or other properties.

Unicode Range Code Example:

Here's a code example of using Unicode ranges in JavaScript regex:

let hanRegex = /[\u4E00-\u9FFF]+/u;
console.log(hanRegex.test('汉字')); // true

let cyrillicRegex = /[\u0400-\u04FF]+/u;
console.log(cyrillicRegex.test('русский')); // true

In this example, the test() function will return true if the string contains at least one Han or Cyrillic character.

Unicode Property Escapes Example:

In JavaScript, Unicode property escapes \p{...} can also be used to match characters that have certain general categories, scripts, or other properties. Here is how you might match Han (Chinese) or Cyrillic characters using properties:

let hanRegex = /\p{Script=Han}+/u;
console.log(hanRegex.test('汉字')); // true

let cyrillicRegex = /\p{Script=Cyrillic}+/u;
console.log(cyrillicRegex.test('русский')); // true

In these examples, \p{Script=Han} matches any character in the Han (Chinese) script, and \p{Script=Cyrillic} matches any character in the Cyrillic script. Note that the u flag is necessary to enable this feature.

How do you exclude a range of characters in regular expressions?​

View Answer:
Interview Response: If we want to exclude a range of characters in a regular expression. We can place the caret ^ character at the start and match any character except the ones we are trying to match.

Code Example:

console.log('alice15@gmail.com'.match(/[^\d\sA-Z]/gi)); // returns @ and .

Do we have to escape special characters in regex sets or ranges?​

View Answer:
Interview Response: In regex sets or ranges, you only need to escape the hyphen (-), caret (^), and the closing bracket ( ] ). For instance, to include a literal hyphen, place it as the first/last character in the set, or escape it with a backslash (-).

Code Example:

// No need to escape
let regexp = /[-().^+]/g;

console.log('1 + 2 - 3'.match(regexp)); // Matches +, -

// Escaped everything
let regexp = /[\-\(\)\.\^\+]/g;

console.log('1 + 2 - 3'.match(regexp)); // also works: +, -
View Answer:
Interview Response: The recommended way to match surrogate pairs in a set or range is using Unicode property escapes with the /u flag. For instance, to match any emoji: /\p{Emoji}/u. Traditional set or range doesn't handle surrogate pairs well.

Code Example:

Certainly! Here's a code example demonstrating how to use Unicode property escapes to match surrogate pairs, specifically for emojis, in JavaScript regex:

let emojiRegex = /\p{Emoji}/u;
console.log(emojiRegex.test('❤️')); // true

let nonEmojiRegex = /[^\p{Emoji}]/u;
console.log(nonEmojiRegex.test('Hello!')); // true

In this example, the test() function is used to check if a string contains any emojis using the \p{Emoji} property escape. The /u flag is necessary to enable full Unicode matching.