Regular expressions (regexp or regex) are used not only by JavaScript developers but also by web analysts for Google Analytics.
.– any single character;\– escape special character meanings (used to escape +, -, ., etc.);[...]– match any character listed inside the square brackets;-– defines a range (for example: [1-9]);^– negates characters that follow it (only works inside square brackets, for example: [^1-9]);^– asserts the start of the string (must be at the beginning);$– asserts the end of the string (must be at the end);?– matches zero or one of the preceding element (for example: 21? matches "2" or "21");+– matches one or more of the preceding element (for example: 21+ matches "21", "211", "2111", etc.);*– matches zero or more of the preceding element (for example: 21* matches "2", "21", "211", "2111", etc.);{min,max}– quantifier specifying minimum and maximum repetitions (for example: 21{2} matches "211" only; 21{1,3} matches "21", "211", "2111" but not "2" or "21111");.*– any sequence of characters of any length;()– groups and captures a subpattern as a group;|– OR operator (for example: 1|2 means "1" OR "2");\d– any digit (same as [0-9]);\s– any whitespace character (space, tab, newline);\w– any word character: letter, digit, or underscore (same as [A-Za-z0-9_]).