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A regular expression is a type of object. It can be either constructed with the RegExp constructor or written as a literal value by enclosing a pattern in forward slash (/) characters.

 let re1 = new RegExp ( "abc" ); let re2 = /abc/ ;

Both of those regular expression objects represent the same pattern: an a character followed by a b followed by a c.

When using the RegExp constructor, the pattern is written as a normal string, so the usual rules apply for backslashes.

The second notation, where the pattern appears between slash characters, treats backslashes somewhat differently. First, since a forward slash ends the pattern, we need to put a backslash before any forward slash that we want to be part of the pattern. In addition, backslashes that aren’t part of special character codes (like \n) will be preserved, rather than ignored as they are in strings, and change the meaning of the pattern. Some characters, such as question marks and plus signs, have special meanings in regular expressions and must be preceded by a backslash if they are meant to represent the character itself.

 let eighteenPlus = /eighteen\+/ ;
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Regular Expressions :: Eloquent JavaScript
s clumsy. But they are a powerful tool for inspecting and processing strings. Properly understanding regular expressions will make you a more effective programmer. Creating a regular expression <span>A regular expression is a type of object. It can be either constructed with the RegExp constructor or written as a literal value by enclosing a pattern in forward slash (/) characters. let re1 = new RegExp("abc"); let re2 = /abc/; Both of those regular expression objects represent the same pattern: an a character followed by a b followed by a c. When using the RegExp constructor, the pattern is written as a normal string, so the usual rules apply for backslashes. The second notation, where the pattern appears between slash characters, treats backslashes somewhat differently. First, since a forward slash ends the pattern, we need to put a backslash before any forward slash that we want to be part of the pattern. In addition, backslashes that aren’t part of special character codes (like \n) will be preserved, rather than ignored as they are in strings, and change the meaning of the pattern. Some characters, such as question marks and plus signs, have special meanings in regular expressions and must be preceded by a backslash if they are meant to represent the character itself. let eighteenPlus = /eighteen\+/; Testing for matches Regular expression objects have a number of methods. The simplest one is test. If you pass it a string, it will return a Boolean telling you whether the string conta


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