CoffeeScript - Regular Expressions

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A regular expression is an object that describes a pattern of characters JavaScript supports. In JavaScript, RegExp class represents regular expressions, and both String and RegExp define methods that use regular expressions to perform powerful pattern-matching and search-and-replace functions on text.

Regular Expressions in CoffeeScript

The regular expressions in CoffeeScript are same as JavaScript. Visit the following link to see the regular expressions in JavaScript − javascript_regular_expressions

Syntax

A regular expression in CoffeeScript is defined by placing the RegExp pattern between the forward slashes as shown below.

pattern =/pattern/

Example

Following is an example of regular expressions in CoffeeScript. In here, we have created an expression that finds out the data that is in bold (data between <b> and </b> tags). Save this code in a file with name regex_example.coffee

input_data ="hello how are you welcome to <b>Howcodex.</b>"
regex = /<b>(.*)<\/b>/
result = regex.exec(input_data)
console.log result

Open the command prompt and compile the .coffee file as shown below.

c:\> coffee -c regex_example.coffee

On compiling, it gives you the following JavaScript.

// Generated by CoffeeScript 1.10.0
(function() {
  var input_data, regex, result;

  input_data = "hello how are you welcome to <b>Howcodex.</b>";

  regex = /<b>(.*)<\/b>/;

  result = regex.exec(input_data);

  console.log(result);

}).call(this);

Now, open the command prompt again and run the CoffeeScript file as shown below.

c:\> coffee regex_example.coffee

On executing, the CoffeeScript file produces the following output.

[ '<b>Howcodex.</b>',
  'Howcodex.',
  index: 29,
  input: 'hello how are you welcome to <b> Howcodex.</b>' ]

heregex

The complex regular expressions we write using the syntax provided by JavaScript are unreadable, therefore to make Regular expressions more readable, CoffeeScript provides an extended syntax for regular expressions known as heregex. Using this syntax, we can break the normal regular expressions using whitespaces and we can also use comments in these extended regular expressions, thus making them more user friendly.

Example

The following example demonstrates the usage of the advanced regular expressions in CoffeeScript heregex. In here, we are rewriting the above example using the advanced regular expressions. Save this code in a file with name heregex_example.coffee

input_data ="hello how are you welcome to Howcodex."
heregex = ///
<b>  #bold opening tag 
(.*) #the tag value
</b>  #bold closing tag
///
result = heregex.exec(input_data)
console.log result

Open the command prompt and compile the .coffee file as shown below.

c:\> coffee -c heregex_example.coffee

On compiling, it gives you the following JavaScript.

// Generated by CoffeeScript 1.10.0
(function() {
  var heregex, input_data, result;

  input_data = "hello how are you welcome to <b> Howcodex.</b>";

  heregex = /<b>(.*) <\/b>/;

  result = heregex.exec(input_data);

  console.log(result);

}).call(this);

Now, open the command prompt again and run the CoffeeScript file as shown below.

c:\> coffee heregex_example.coffee

On executing, the CoffeeScript file produces the following output.

[ '<b>Howcodex.</b>',
  'Howcodex.',
  index: 29,
  input: 'hello how are you welcome to <b>Howcodex.</b>' ]
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