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JS-Grammar

Regular expression​

Syntax​

Brackets​

Patterns that find a range of characters in the string

  • [...] Any of the characters encapsulated.
  • [^...] Not any character encapsulated.
  • [0-9]
  • [a-z]

Quantifiers​

Special characters or flags that specify the position or frequency of a certain pattern

Frequency​
  • p+ one or more times
  • p* zero or more times
  • p? maximum once
  • p{n} in a sequence n times
  • p{m,n} minimum m times and max n times
Positional​
  • ^p p should exist at the start of the string
  • p$ p should exist at the end of the string.

Lookaround​

Assertions that see if a character match is possible or not, and accordingly return boolean values without consuming any part of the string.

  • p(?=q)p(?=q) Assert that p should be immediately be followed by q
  • p(?!q)p(?!q) Assert that p should NOT be immediately followed by q
  • p(?<=q)p(?<=q) Assert that p should immediately be preceded by q
  • p(?<!q)p(?<!q) Assert that p should NOT immediately be preceded by q

Character literals​

representations for characters and special characters.

  • Alphanumeric Any alphabet or numeric character itself e.g. a is any character which is the letter a
  • \0 A null character
  • \t A tab character
  • \n A newline character
  • \v A vertical tab character
  • \f A form feed character (next page character)
  • \r A carriage return character

Metacharacters​

character representations for a group of characters falling under the same categories.

  • . Any single character ([^\n])
  • \s A white space character like tab and spaces ([ \n\r\t\f])
  • \S Any character which is not a white space character ([^ \n\r\t\f])
  • \d Any numeric character ([0-9])
  • \D Any non-numeric character ([^0-9])
  • \w Any word character ([a-zA-Z0-9_])
  • \W Any non-word character ([^a-zA-Z0-9_])

RegExp object​

exec method​

It runs the regular expression on a string passed as an argument and returns the found text as an object

test method​

It runs the regular expression on a string passed as an argument and returns a boolean value telling if a match was found or not.

String methods with RE​

Search method​

It takes a query-string as an argument and searches within the string to return the character index at which the query-string starts. It returns “-1” if no match is found.

replace method​

It takes a query-string as an argument and searches within the string to replace the matching substring.

RE example​

// Check if the password is strong password.
// Length: .{6,} (Minimum 6 characters)
// Uppercase letter: .*[A-Z] (A-Z)
// Lowercase letter: .*[a-z] (a-z)
// Numeric digit: .*\d (0-9)
// Special Character: .*[\W] (any character other than {0-9, a-z, A-Z})
var isSafe = function(password)
{
    var regex = /^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[\W]).{6,}$/; 
    return regex.test(password); // return regex.test(password) after completing regex
}