Browser compatibility issues in JS

This article mainly introduces the relevant information of the DOMContentLoaded event that JS is compatible with all browsers. In standard browsers, we can use the DOMContentLoaded event to achieve our requirements. It is also extremely simple to register the event processing function. Interested friends can learn together. Bar

When using JavaScript to operate dom elements, the code for obtaining dom elements is usually placed in the window.onload=function(){}event event processing function, but window.onload The event may affect the customer experience after some start, because you have to wait for all scripts, css code, images and other content to be loaded before this event is triggered, especially if the amount of images is large, it will seriously affect the customer experience. So many times, you only need the DOM structure to be loaded. jQuery's $(document).ready(function(){}) implements this function. Here is an introduction to how native JavaScript implements this function.

Introduction to the implementation process:

#In standard browsers, we can use the DOMContentLoaded event to achieve our requirements, and registering event processing functions is also extremely simple. .

The code is as follows:

addEventListener(‘DOMContentLoaded',fn,false)

However, IE8 and browsers below IE8 do not support the DOMContentLoaded event, so another way is needed to solve this problem.

Many friends may think that whether the document.readyState status of the document.onreadystatechange event is equal to complete is used to determine whether the dom structure is loaded. However, the task cannot be completed after testing. If the page uses an iframe to introduce subpages, there will be problems. .

The solution is as follows:

The doScroll method unique to lower versions of IE browsers. When the dom structure has not been loaded, calling this method will Report an error, so you can continuously call this method through the timer function, and combine it with the try catch statement to implement the judgment function. The code is as follows:

eventQueue = [];
isReady = false;
isBind = false;
function domReady(fn){
 if(isReady){
  fn.call(window);
 }
 else{
  eventQueue.push(fn);
 };
 bindReady();
};
function bindReady(){
 if(isReady) return;
  if(isBind) return;
  isBind=true;
  if(window.addEventListener){
   document.addEventListener('DOMContentLoaded',execFn,false);
  }
  else if(window.attachEvent){
   doScroll();
  };
};
function doScroll(){
 try{
  document.documentElement.doScroll('left');
 }
 catch(error){
  return setTimeout(doScroll,20);
 };
 execFn();
};
function execFn(){
 if(!isReady){
  isReady=true;
  for(var index=0;i<eventQueue.length;index++){
   eventQueue[index].call(window);
  };
  eventQueue = [];
 };
};
domReady(function(){
 //code
});
domReady(function(){
 //code
});

The code implements the DOMContentLoaded effect that is compatible with all browsers. Here is an introduction to it Implementation process.

1. Code comments:

(1).eventQueue = [], declare an empty array for the function queue to be executed .

(2).isReady = false, declare a variable and assign the initial value to false. If it is true, it means that the dom has been loaded.

(3).isBind = false, declare a variable and assign the initial value to false. If it is true, it means that the time processing function is bound.

(4).function domReady(fn){}, this function implements the function of waiting for the dom to be loaded before executing the fn function.

(5).if(isReady){fn.call(window);}, if the variable value is true, execute the function directly.

(6).else{eventQueue.push(fn);}, add the function to be executed to the array.

(7).bindReady(), this function can realize the registration event processing function.

(8).if(isReady) return, if equal to true, jump out of the function directly. At this time, the fn function has been executed.

（9）.if(isBind) return, if it has already been registered, there is no need to do it a second time.

(10).isBind=true, change the value of the variable to true.

（11）.if(window.addEventListener){document.addEventListener('DOMContentLoaded',execFn,false);}, if it is a standard browser, use addEventListener to register the event processing function.

(12).else if(window.attachEvent){doScroll();}, if the browser is IE8 or below, call the doScroll method to achieve this effect.

(13).function doScroll(){}, this function can use the timer function to continuously call the doScroll() function. If an error is reported, continue to call, otherwise, the dom structure is loaded. So the relevant functions are executed.

（14）.function execFn(){}, this function can take out the function to be executed from the array, then execute it, and finally clear the array.

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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