On a medium-sized site, you may want your javascript all in the same file, but only process certain functions based on element presence.

page_management.js

/**
 * Internal page management
 * Add selector-dependent js to the array
 *   or call page to execute all js relevant to the current page
 * @param {String} selector A jQuery selector
 * @param {Function} fn A function to execute if sel is present on the page
 */

var pages = [];
var page = function( selector, fn ) {
	var cur, $sel;
	if ( selector ) {
		pages.push({ selector: selector, fn: fn });
	} else {
		while ( cur = pages.shift() ) {
			$sel = $(cur.selector);
			if ( $sel.length ) {
				cur.fn.call( $sel, $sel );
			}
		}
	}
};

page("#foo", function() {
	// This only runs on a page with the element #foo on it
});

page("#someTable td", function() {
	// The context of this function is the jQuery selection
	this.each(function() { });
});

page("#someForm", function( $form ) {
	// Conditionally load scripts that pertain only to #someForm
	// The selection is also passed as an argument( $form )
	require([ 'jquery.validate' ], function() {
		$form.validate();
	});
});

$(document).ready(page);