jQuery document.ready vs self calling anonymous function

2020/11/18 10:42 · javascript ·  · 0评论

What is the difference between these two.

  1. $(document).ready(function(){ ... });

  2. (function(){ ... })();

Are these both functions called at the same time?
I know, document.ready will be triggered when the entire HTML page is rendered by the browser but what about 2nd function (self calling anonymous function). Does it wait for browser to complete rendering the page or it is called whenever it is encountered?

  • $(document).ready(function(){ ... }); or short $(function(){...});

    This Function is called when the DOM is ready which means, you can start to query elements for instance. .ready() will use different ways on different browsers to make sure that the DOM really IS ready.

  • (function(){ ... })();

    That is nothing else than a function that invokes itself as soon as possible when the browser is interpreting your ecma-/javascript. Therefor, its very unlikely that you can successfully act on DOM elements here.

(function(){...})(); will be executed as soon as it is encountered in the Javascript.

$(document).ready() will be executed once the document is loaded. $(function(){...}); is a shortcut for $(document).ready() and does the exact same thing.

  1. $(document).ready(function() { ... }); simply binds that function to the ready event of the document, so, as you said, when the document loads, the event triggers.

  2. (function($) { ... })(jQuery); is actually a construct of Javascript, and all that piece of code does is pass the jQuery object into function($) as a parameter and runs the function, so inside that function, $ always refers to the jQuery object. This can help resolve namespacing conflicts, etc.

So #1 is executed when the document is loaded, while #2 is run immediately, with the jQuery object named $ as shorthand.

The following code will be executed when the DOM (Document object model) is ready for JavaScript code to execute.

$(document).ready(function(){
  // Write code here
}); 

The short hand for the above code is:

$(function(){
  // write code here
});

The code shown below is a self-invoking anonymous JavaScript function, and will be executed as soon as
browser interprets it:

(function(){
  //write code here
})();   // It is the parenthesis here that call the function.

The jQuery self-invoking function shown below, passes the global jQuery object as an argument
to function($). This enables $ to be used locally within the self-invoking function without needing
to traverse the global scope for a definition. jQuery is not the only library that makes use of $, so this
reduces potential naming conflicts.

(function($){
  //some code
})(jQuery);

document.ready run after DOM is "constructed". Self-invoking functions runs instantly - if inserted into <head>, before DOM is constructed.

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