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Compiles a regular expression into an internal format for faster execution.


rgExp.compile( pattern , [ flags ] )
Required. An instance of a Regular Expression object. Can be a variable name or a literal.
Required. A string expression containing a regular expression pattern to be compiled
Optional. Available flags, which may be combined, are: g (global search for all occurrences of the pattern), i (ignore case), m (multiline search), u (Unicode), y (sticky matching),


The following example illustrates the use of the compile method:

function CompileDemo(){
    var rs;
    var s = "AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPp"
    // Create regular expression for uppercase only.
    var r = new RegExp("[A-Z]", "g");
    var a1 = s.match(r)              // Find matches.
    // Compile the regular expression for lowercase only.r.compile( "[a-z]" , "g" ) ;
 // Find matches.
    var a2 = s.match(r)
    return(a1 + "\n" + a2);


The compile method converts pattern into an internal format for faster execution. This allows for more efficient use of regular expressions in loops, for example. A compiled regular expression speeds things up when reusing the same expression repeatedly. No advantage is gained, however, if the regular expression changes.


  • Microsoft Developer Network: Article