Starting point

Typically, jQuery is used by putting initialization code and event handling functions in $(_handler_). This is triggered by jQuery when the browser has finished constructing the DOM for the current Web page.

$(function () {
        // This anonymous function is called when the page has completed loading.
        // Here, one can place code to create jQuery objects, handle events, etc.
});

or

$(fn); // The function named fn, defined elsewhere, is called when the page has loaded.

Historically, $(document).ready(callback) has been the de facto idiom for running code after the DOM is ready. However, since jQuery 3.0, developers are encouraged to use the much shorter $(handler) signature instead.