I can’t think of a question I asked. Take a look?

1. Js prevents time bubbling by default:

1) Event.stopPropagation () prevent event bubblings (), prevent time from spreading to document, but default event preventDefault()return false; Prevents both event bubbling and default eventsCopy the code

2. Logic code, you can print it out and see oh, the answer is in the comments

Var a = [1, 2]; Var b = a.c oncat ([3, 4, [5, 6]]). 1. What is the length of array B?Copy the code

var data = [];
for(var i = 0; i<3; i++){ data[i] =function(){ console.log(i); }} 2, data[0] =? data[1] = ? data[2] = ?Copy the code

var z = 10;
function foo(){
    console.log(z);
}
(function(funArg){ var z = 20; funArg(); })(foo) console.log(z); / / 3, z =?Copy the code

function fact (num){ 
    if(num<=1){ 
	return1}else{
	returnnum*arguments.callee(num-1) } } var anotherFact = fact; fact =null console.log(anotherFact(4)); / / 4, (anotherFact (4)?Copy the code

3. There is a place I don’t understand: arguments.callee

• Firstly, what are arguments?
• Arguments is an array-like but non-array object created during a function call, and stores the arguments actually passed to the function, not just the list of arguments declared by the function.

Arguments. callee is a recursive algorithm that implements computing factorial functions, however

Apply ([thisObj [,argArray]]);Copy the code

Syntax: call([thisObject[,arg1 [,arg2 [,...,argn]]]]);Copy the code

5. Browser event stream:

1. The event bubbling
1. Events are initially received by the most specific element (the node with the deepest nesting level in the document) and then propagated up the hierarchy to the less specific nodes
   
   
2. Event capture
1. The idea of event capture is that less specific nodes should receive events earlier, while the most specific nodes should receive events last. The intent of event capture is to catch an event before it reaches its intended destination
   
   
3. The DOM event flow
1. Between the capture phase and the event bubble phase

6. Improve web page performance

• Reduce HTTP requests:
• Image loading will also produce HTTP requests, so it is recommended to minimize the use of network images, if there are many images, use font ICONS
• Using CDN address:
• A CDN (Content Delivery network) is a set of Web servers distributed in multiple geographic locations to deliver content to users more efficiently. When optimizing performance, the selection of servers to deliver content to specific users is based on measurement of online MOOCs congestion.
• CDN can also back up data, expand storage capacity, and cache data. CDN also helps ease Web traffic peak pressure.
• Put the style sheet in the header
• Reduce the time for the first screen to gradually display the page content, improve user experience, and prevent the “white screen”. Being able to display content as quickly as possible and provide visual feedback is important for users with slow Internet connections
• Place the script at the bottom
• As with style sheets, placing them at the bottom reduces the time the first screen appears. The download and execution of JS blocks the building of the Dom tree (or, more precisely, interrupts the updating of the Dom tree), so the script tag placed in an HTML section within the first screen will truncate the content of the first screen
• Avoid CSS expressions
• CSS expressions are a powerful and dangerous way to dynamically set CSS properties, supported by IE5 and later, before IE8.
• Use external JavaScript and CSS
• Inline scripts or styles can reduce HTTP requests and, in theory, speed up page loading. In practice, however, when scripts or styles are imported from outside the file, it is possible for the browser to cache them so that they can be used directly for later loading, while the SIZE of the HTML document is reduced to speed up loading.

7.HTTPS vs. HTTP: