A few notes when writing javascript in pagespeed optimization


Never use function document.write to append HTML on the document, use the jQuery function instead $('body').append


See all javascript events below:

//ready document
//all js in page ready include jquery
_HWIO.readyjs(function(){ });
//window ready event
_HWIO.winReady(function(){ });
//wait for exist `jQuery` object
}, ['jQuery']/*, 500,20, 'custom-name'*/);
//your code
}, function(){
return typeof jQuery!='undefined';

Run script with conditional:

//check for exist variable
}, ['cookie']);
//run suddenly after this js (handle) has loaded
console.log("~~ ready js-cookie")
//execute when user got interactive such as mouse move, click,scroll..
_log('@when interactive');

To know JS, CSS name (handle) you can right-click on your page > select "View page source" > find the JS or CSS URL you want to find the handle name. You can see id="example-xxx-js" or id="example-yyy-css" => the "example-xxx" and "example-yyy" will be JS handle name or CSS handle name of that JS/CSS file.

We will merge all JS and CSS to one file and load it lazy a bit. You can also find the original JS files by adding parameters ?merge_js=0 at the end of the URL. Same for CSS ?merge_css=0

In addition, you may want to specify which JS code will run immediately and delay until the user interacts on the web page.

//combine php hook `hpp_delay_it_script`
_HWIO.add_event('run_script', function(v, js){
//when interactive
if( js.indexOf('ready js-cookie')!==-1)return 0;
return v;

Before executing any Javascript code, there is a core inline JS that is placed at the top of the page. And you will want to append your inline js after it, then use hpp_print_initjs hook - an example:

add_action('hpp_print_initjs', function(){
#if(is_home() || is_front_page())
if(isset($GLOBALS['hpp-criticalfile'])) {
_HWIO.add_event('hpp_allow_js', function(v,att){
return att.l.endsWith('.less') || att.l.endsWith('.html') || (location.href.indexOf('merge_js=0')===-1 && (att.l.indexOf('')!==-1 || att.l.indexOf('jquery.min.js')!==-1))? 0:v;

the event hpp_allow_js to allow / not allow, decide which JS file should be run or not.