express.js routes explanation

Question

I was looking at express.js source code, to find out how it maps named route parameters to req.params properties.

For those who don\'t know, in exp

Answer 1

It is for matching file extensions and such properly.

Given the path '/path/:file.:ext', consider the difference between the expressions:

// With 'format' checking
/^\/path\/(?:([^\/]+?))(?:\.([^\/\.]+?))\/?$/

// Without 'format' checking
/^\/path\/(?:([^\/]+?))(?:([^\/]+?))\/?$/

In the first case, you end up with params as

{
    file: 'file',
    ext: 'js'
}

but without the format checking, you end up with this:

{
    file: 'f',
    ext: 'ile.js'
}