Regex in JavaScript

/error/i

# Declare a regex using JavaScript literal syntax.

new RegExp("^" + prefix + "\\d+$", "i")

# Build a regex dynamically from strings.

/error/i.test(message)

# Check whether a regex matches a string.

/(\d{4})-(\d{2})-(\d{2})/.exec(dateStr)

# Get captures and index information from a match.

text.match(/\b\w+\b/g)

# Match against a string and return results.

Array.from(text.matchAll(/(?<key>\w+)=(?<val>\w+)/g))

# Iterate all matches with captures.

text.replace(/\s+/g, " ")

# Replace matched text using a regex.

text.replace(/(\w+),\s*(\w+)/g, (_, last, first) => `${first} ${last}`)

# Compute replacements dynamically from captures.

csvLine.split(/\s*,\s*/)

# Split a string using a regex delimiter.

/pattern/gimsuyd

# Global, ignore-case, multiline, dotAll, Unicode, sticky, indices.

/(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/

# Capture with a descriptive group name.

/(?<q>["\']).*?\k<q>/

# Backreference a named capture.

text.replace(/(\w+)\s+(\w+)/, "$2, $1")

# Use `$1`, `$2`, etc. in replacement strings.

text.replace(/(?<h>\d{2}):(?<m>\d{2})/, (...args) => { const groups = args.at(-1); return `${groups.h}h ${groups.m}m`; })

# Use a replacement callback to access named captures clearly.

/^\p{L}+$/u

# Match Unicode letters or scripts in JS.

/^[^\s@]+@[^\s@]+\.[^\s@]+$/

# Check a simple email-like structure.

/^[a-z0-9]+(?:-[a-z0-9]+)*$/

# Match lowercase slugs with hyphens.

/([^&=?#]+)=([^&=#]*)/g

# Extract query-like key-value pairs.

text.trim().replace(/\s+/g, " ")

# Normalize repeated whitespace down to single spaces.

text.replace(/\bBearer\s+[A-Za-z0-9._-]+\b/g, "Bearer [REDACTED]")

# Mask bearer tokens in logs.

/#(?:[0-9A-Fa-f]{3}|[0-9A-Fa-f]{6}|[0-9A-Fa-f]{8})\b/g

# Extract CSS-like hex color literals.

/^(?<major>0|[1-9]\d*)\.(?<minor>0|[1-9]\d*)\.(?<patch>0|[1-9]\d*)(?:-[0-9A-Za-z.-]+)?(?:\+[0-9A-Za-z.-]+)?$/

# Extract version parts from a semantic version string.