Regular Expressions (Regex) with JavaScript - Easy and Fast!

Explore the interactive learn regex tool to visualize patterns, match results, splits, and replacements in JavaScript, using the repository data, usage examples, and cheat sheet.

Master single character patterns in regex, using global and case-insensitive flags, literals, sets, and ranges. Apply escaping, control characters, hex and Unicode codes, and note anchors.

Explore anchors in JavaScript regex, using word boundary matches, start and end of string anchors, and multiline mode to detect matches at line starts and ends for input validation.

Explore character classes in JavaScript regex, using digits with \d, non-digits with \D, word, nonword, whitespace, and Unicode categories to match digits and letters across languages.

Explore regular expression quantifiers in JavaScript, learning how to make parts optional or required, constrain repetitions with * + ? and {n,m}, and use word boundaries to refine matches.

Learn to validate HTML form input with a JavaScript regex using the pattern attribute, including five-digit or nine-digit zip codes with a dash.

Build and validate zip codes using a JavaScript regex pattern that matches five digits with an optional dash and four digits, applied via the HTML input pattern attribute.

Discover how the regular expression engine evaluates patterns and text one character at a time, left to right, using greedy, lazy, and backtracking, with groups and lookahead and lookbehind.

Master left-to-right regex evaluation and how the engine prioritizes the leftmost pattern before backtracking to alternatives. Use word boundaries and grouping to match exact words like car or carpet efficiently.

Explore left-to-right evaluation of patterns and text, and see how order affects matches with carpet and car. Extract common subexpressions and use word boundary to reduce backtracking and improve precision.

Explore greedy and lazy quantifiers and backtracking in regular expressions, illustrated by an I-10 analogy from LA to Phoenix to Jacksonville, with plus, star, and question mark behavior.

Explore greedy versus lazy quantifiers in regex, and see how backtracking shapes pattern matching to extract trailing numbers and match word variants like apple pastry, apple paste, or apple pie.

Explores greedy and lazy quantifiers in JavaScript regex, demonstrating end-of-sentence digit capture, backtracking fixes with precise patterns, and showcases case-insensitive searches for apple pastry, paste, or pie using word boundaries.

Learn how groups in regular expressions break patterns into subpatterns, mark parts as optional or repeating, use named or non-capturing groups, apply back references, and perform replacements to reformat text.

Explore building regex patterns to match numbers with decimals and thousands separators, use non capturing groups to clean matches, and apply backreferences and replacements to detect and remove duplicate words.

Explore look ahead and look behind as zero width assertions that check upcoming or preceding characters without consuming them, enabling conditional logic like a valid password and multilingual word matching.

Explore look behind in regex, using positive and negative look behind to enforce preconditions and extract only the desired text, such as four-letter product codes followed by digits.

Learn how exponential degradation arises from poorly written regex patterns, backtracking, and group-level repetition, and apply fixes like removing group repetition or adding word boundaries.

Enhance regex performance by removing the outer group repetition and adding boundaries to prevent exponential delays on partial matches. Conduct positive and negative tests for near-zero runtime.

Learn JavaScript's regex capability with string and RegExp objects, exploring operations and pattern representation. Use Visual Studio Code and Chrome for debugging, breakpoints, console output, and the source property.

Use the string search method to find digits with \d and +, returning the first index. Compare regex objects and string literals, noting escaping backslashes for valid input validation.

Validate user input with regular expressions by checking integers using a start and end anchored digit pattern, implement a unit test, and discuss performance considerations.

Explore the JavaScript regex capabilities with match and matchAll, learn to use the global flag, and extract values with groups and named groups for robust text parsing.

Learn to perform find and replace with regex in JavaScript, using named capture groups and dollar-name references to reformat dates, and explore replacement functions and split patterns.

learn how the JavaScript regex object uses exec and test to find and validate matches, and how to iterate with the global flag, extract groups, and view match details.

Learn to parse robocopy log files and convert them to JSON by extracting source and destination paths, metrics from the header table, and any error messages using three patterns.

Learn to build regex patterns for Robocopy logs, capturing source and destination paths with named groups, and extract errors, timestamps, and table metrics using multi-line, case-insensitive searches.

Learn to convert unstructured log data to json using JavaScript regex. Build a RoboCopy log parser that extracts directory paths, matrix data, and errors into a structured json output.

Use regular expressions to parse sensor data, extracting dates and temperature-humidity pairs, with two patterns for header and pairs and a later json conversion.

Learn regex patterns for sensor data: capture date with named year, month, day groups, and extract temperature and humidity values, using separate header and measurement patterns.

Learn how to parse sensor data using regex in JavaScript to convert date, temperature, and humidity values into json, with examples from the sensor data solution html and shell.

Learn to convert hospital HTML reports into JSON using JavaScript regex, by cleaning HTML, extracting rows, and parsing cell values for lab results and problems data.

Apply regex patterns to health care HTML tables to capture lab results and problems data, cleaning spaces and extracting row and cell values.

Learn to parse health care table data into json using regex patterns, with a walkthrough of escaping html tags and producing json output.