pagex 
pagex(path, [negate], callback, [pathname]);
// Call a function if the current page is exactly `/users`
pagex('/users', () => {
// ...
});
// Execute only if the current page is exactly `/books`
if (pagex('/books')) {
// ...
}Due to the API that it has, it's also highly compatible with React (though purely accidentally):
// Basic routing in React
export default () => (
<div>
{pagex('/', () => <Homepage />)}
{pagex('/books', () => <Library />)}
{pagex('/books/:id', id => <Book id={id} />)}
</div>
);Parameters
pagex(path, [callback = (...a) => a], [negate = false], [url = window.location.pathname]);path: the path or regex to be matched against the current url. This is the only required parameter and it has to be the first one.callback = (...args) => args(optional): the function that will be called if the path matches (or if it doesn't and it's negated). Any value returned here will be the final value returned bypagex(). The default function will return an array if matched, with any matched parameter inside. So it's always truthy when it's matched so you can doif (pagex('/hello')) {...}.negate = false(optional): set to true to call the function if NOT in this path. Really useful for the difficulty to do so otherwise in RegExp.url = window.location.pathname(optional): the url path to compare it against. Will default to the current browser pathname if it's not provided.
Note: the callback, negate and url can be in any order since they are of different type. The path always has to be the first argument though.
Pseudo Example
If you have a large javascript codebase, you can split it the following way:
// Logic for all your pages. For example, analytics
analytics();
// Logic specific for your /users page and subpages
pagex('/users', function(){
// ...
});
// Logic specific for your /books page and subpages
pagex('/books', function(){
// ...
});Path
A simple front-end router based on express.js router, which is based on path-to-regexp:
pagex('/hi', function(){
alert('Hi there!');
});You can get the url parameters easily:
pagex('/users/:username', function(username){
alert('Hi there ' + username + '!');
});Make them optional:
// Note: ES6 default parameter shown here
pagex('/users/:username?', function(username = 'everyone'){
alert('Hi there ' + username + '!');
});Regex
Originally the main way of doing this was with pure regex (that's why it's called pagex, from Page + Regex). However, the main way now is with paths that get converted internally to regex. If you want to use regex you can do so:
// Starts by a string
pagex(/^\/user/, function(){
console.log("User section loaded");
});
// When NOT in this page, since negating in regex is complex: stackoverflow.com/a/1240337
pagex(/^\/user/, true, function(){
console.log("User index");
});
// Strict page
pagex(/^\/user$/, function(){
console.log("User index");
});
// Parameters from capturing groups, with required id
pagex(/^\/user\/([A-Za-z0-9]+)/, function(id){
console.log("Hello user " + id + "!");
});
// Parameters from capturing groups, with optional id
pagex(/^\/user\/?([A-Za-z0-9]+)?/, function(id){
console.log("Are you there, user " + id + "?");
});