Javascript

A few notes when writing javascript in pagespeed optimization

document.write

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

Events

See all javascript events below:

//ready document
_HWIO.docReady(function(){});

//all js in page ready include jquery
_HWIO.readyjs(function(){ });

//window ready event
_HWIO.winReady(function(){ });

//wait for exist `jQuery` object
_HWIO.waitForExist(function(){
  jQuery('.woocommerce-product-gallery').css('opacity','');
}, ['jQuery']/*, 500,20, 'custom-name'*/);

_HWIO.waitForExist(function(){
  //your code
}, function(){
  return typeof jQuery!='undefined';
});

Run script with conditional:

//check for exist variable
_HWIO.readyjs(function(){
	cookie.set('a',1);
}, ['cookie']);	

//run suddenly after this js (handle) has loaded
_HWIO.readyjs('js-cookie',function(){
  console.log("~~ ready js-cookie")
});

//execute when user got interactive such as mouse move, click,scroll..
_HWIO.readyjs(null,function(){
	_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;
});
	</script>
	<?php
});

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('code.jquery.com')!==-1 || att.l.indexOf('jquery.min.js')!==-1))? 0:v;
});
	<?php
	}
});

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