Question

I am curious about the use of the function named test (line 3) below:

var pattern = /[1-9][1-9]{5}/;
var str = 'this is 248760!';
alert(pattern.test(str));

I saw this script in a book and there is no definition of the test(str) function.

Why does it alert true instead of giving an error?

Answer 1

pattern is a regular expression object

/[1-9][1-9]{5}/.test("foo"); // valid javascript

A regular expression object provides many member functions such as test(...) and toString() to name a few…

/[1-9][1-9]{5}/.toString(); // "/[1-9][1-9]{5}/"

The /‘s at the beginning and end are kind of a short hand for the following:

new RegExp("[1-9][1-9]{5}"); // /[1-9][1-9]{5}/