$(document).ready equivalent without jQuery

Question

I have a script that uses $(document).ready, but it doesn't use anything else from jQuery. I'd like to lighten it up by removing the jQuery dependency.

How can I implement my own $(document).ready functionality without using jQuery? I know that using window.onload will not be the same, as window.onload fires after all images, frames, etc. have been loaded.

Answer 1

How about this solution?

// other onload attached earlier
window.onload=function() {
   alert('test');
};

tmpPreviousFunction=window.onload ? window.onload : null;

// our onload function
window.onload=function() {
   alert('another message');

   // execute previous one
   if (tmpPreviousFunction) tmpPreviousFunction();
};

Answer 2

Here is the smallest code snippet to test DOM ready which works across all browsers (even IE 8):

r(function(){
    alert('DOM Ready!');
});
function r(f){/in/.test(document.readyState)?setTimeout('r('+f+')',9):f()}

See this answer.

Answer 3

I simply use:

setTimeout(function(){
    //reference/manipulate DOM here
});

And unlike document.addEventListener("DOMContentLoaded" //etc as in the very top answer, it works as far back as IE9 -- http://caniuse.com/#search=DOMContentLoaded only indicates as recently as IE11.

For instance, go to https://netrenderer.com/index.php, choose Internet Explorer 9 from the dropdown, enter https://dexygen.github.io/blog/oct-2017/jekyll/jekyll-categories/liquid-templates/2017/10/22/how-jekyll-builds-site-categories.html and click "Render", and you will see something akin to the screenshot at the bottom of this post.

See the following Javascript code I am using in the header to manipulate the style of the Jekyll "hacker" theme to my liking -- in particular you can reference the if (location.pathname !== rootPath) block to see how I am inserting the Home and Blog Home links, which are being displayed by IE9 per the NetRenderer site.

Interestingly I stumbled upon this setTimeout solution in 2009: Is checking for the readiness of the DOM overkill?, which probably could have been worded slightly better, as I meant by using various frameworks' more complicated approaches.

setTimeout(function() {//delay execution until after dom is parsed
    var containerEls = document.getElementsByClassName('container');
    var headingEl = containerEls[0].getElementsByTagName('h1')[0];
    var headerEl = document.getElementsByTagName('header')[0];
    var downloadsSectionEl = document.getElementById('downloads');
    var rootPath = "/";
    var blogRootPath = "/blog/";

    containerEls[0].style.maxWidth = '800px';
    containerEls[1].style.maxWidth = '800px';
    headingEl.style.margin = '0';
    headerEl.style.marginBottom = '7px';
    downloadsSectionEl.style.margin = '0';

    if (location.pathname !== rootPath) {
        downloadsSectionEl.appendChild(generateNavLink('Home', rootPath));
        if (location.pathname !== blogRootPath) {
            downloadsSectionEl.appendChild(document.createTextNode(' | '));
            downloadsSectionEl.appendChild(generateNavLink('Blog Home', blogRootPath));
        }
    }

    function generateNavLink(linkText, hrefPath) {
        var navLink = document.createElement('a');
        var linkTextNode = document.createTextNode(linkText);
        navLink.setAttribute('href', hrefPath);
        navLink.appendChild(linkTextNode);
        return navLink;
    }
});

Answer 4

If you don't have to support very old browsers, here is a way to do it even when your external script is loaded with async attribute:

HTMLDocument.prototype.ready = new Promise(function(resolve) {
   if(document.readyState != "loading")
      resolve();
   else
      document.addEventListener("DOMContentLoaded", function() {
         resolve();
      });
});

document.ready.then(function() {
   console.log("document.ready");
});

Answer 5

Place your <script>/*JavaScript code*/</script> right before the closing </body> tag.

Admittedly, this might not suit everyone's purposes since it requires changing the HTML file rather than just doing something in the JavaScript file a la document.ready, but still...

Answer 6

The setTimeout/setInterval solutions presented here will only work in specific circumstances.

The problem shows up especially in older Internet Explorer versions up to 8.

The variables affecting the success of these setTimeout/setInterval solutions are:

1) dynamic or static HTML
2) cached or non cached requests
3) size of the complete HTML document
4) chunked or non chunked transfer encoding

the original (native Javascript) code solving this specific issue is here:

https://github.com/dperini/ContentLoaded
http://javascript.nwbox.com/ContentLoaded (test)

this is the code from which the jQuery team have built their implementation.