It is recommended to use this form only when creating regex from dynamic variables.
Use when the expression may change or the expression is user generated.
var re = new RegExp(".*");
With flags:
var re = new RegExp(".*", "gmi");
With a backslash: (this must be escaped because the regex is specified with a string)
var re = new RegExp("\\w*");
Use when you know the regular expression will not change, and you know what the expression is before runtime.
var re = /.*/;
With flags:
var re = /.*/gmi;
With a backslash: (this should not be escaped because the regex is specified in a literal)
var re = /\w*/;