Javascript Regular Expressions character class

Introduction

Character class means digits, letters, and whitespace characters.

The special characters are displayed in the following table:

Character Characters Class
 It Matches
 Example
\d
 Any digit from 0 to 9
 \d\d matches 72, but not aa or 7a.
\D
 Any character that is not a digit
 \D\D\D matches abc, but not 123 or 8ef.
w

 Any word character; that is, A-Z, a-z, 0-9,
and the underscore character (_)
\w\w\w\w matches Ab_2, but not $% or Ab_@.

\W
 Any non-word character
 \W matches @, but not a.
\s

 Any whitespace character

 \s matches tab, return,
formfeed, and vertical tab.
\S

 Any non-whitespace character

 \S matches A, but not the
tab character.
.

 Any single character other than the newline
character (\n)
. matches a or 4 or @.

[...]


 Any one of the characters between the
brackets[a-z] matches any character in the
range a to z
[abc] matches a or b or c,
but nothing else.

[^...]




 Any one character, but not one of those
inside the brackets



[^abc] matches any
character except a or b or c.
[^a-z] matches any
character that is not in the
range a to z.

To match a telephone number in the format 1-800-888-1234, the regular expression would be as follows: 

\d-\d\d\d-\d\d\d-\d\d\d\d

The following code checks that a pass phrase contains only letters and numbers-that is, alphanumeric characters, not punctuation or symbols like @, %, and so on: 

let input = "this is a test"; 

function isValid (text) { 
   let myRegExp = /[^a-z\d ]/i; 
   return  !(myRegExp.test(text)); 
} 

if (isValid(input)) { 
   console.log("Your text contains only valid characters"); 
} else { //from  w ww  .  j ava  2  s.c o m
   console.log("Your text contains one or more invalid characters"); 
}

Let's see how this translates into a regular expression:

1.You use square brackets with the ^ symbol: 

[^]

This means you want to match any character that is not one of the characters specified inside the square brackets.

2. You add a-z, which specifies any character in the range a through z: 

[^a-z]

So far, your regular expression matches any character that is not between a and z.

Because you added the i to the end of the expression definition, you've made the pattern case-insensitive.

So your regular expression actually matches any character not between A and Z or a and z.

3.You add \d to indicate any digit character, or any character between 0 and 9: 

[^a-z\d]

4.Your expression matches any character that is not between a and z, A and Z, or 0 and 9.

You decide that a space is valid, so you add that inside the square brackets: 

[^a-z\d ]

Putting this all together, you have a regular expression that matches any character that is not a letter, a digit, or a space.




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