For loops and functions

for loop ：

Concept ： Do repetitive things , Usually associated with numbers

The basic structure ：for(;;){}( Two semicolons cannot be omitted )

One 、for Pay attention

• Whether the conditions are met ：（ If not satisfied , The code is not executed at one time ）
• Is there an end condition （ without , It's a dead cycle （ Wireless loop ））
• browser 15 Seconds have not reacted , Will automatically crash

Two 、break

• break stay for Just... In the loop break The code is executed for Cycle and termination

3、 ... and 、continue

• continue When this cycle continue The code after the keyword does not execute the next cycle

var i = 1;
	 for(i=1;i<=500;i++){
	 console.log(i);
}

var ps = document.querySelectorAll("p");
	for(var i=0;i<ps.length;i++){
		ps[i].onclick = function(){
			alert(this.innerHTML);
			this.classList.toggle("active");// Switch active Class name 
		}
	}

var ps = document.querySelectorAll("p");
	for(var i=0;i<ps.length;i++){
	    console.log(ps[i].innerHTML);
	}

function ：

One 、 Defined function

• function name (){ Code }
• A function is a block that can be executed repeatedly （ call ） Code block for

function fun(){
	console.log(" Raising sheep ");
	console.log(" Feed the horse ");
	console.log(" Kindling wood ");
	console.log(" eagle ");
}

Two 、 Call function

• 1. stay js Call directly ：fun()
• 2. Sure html Event properties ：<h1 οnclick="fun()">
• 3.dom1 Level event registration ：btn.onclick = fun
• 4.dom2 Level event registration ：btn.addEventListener("click",fun)
• 5. Calling function in function

function fun(){
	console.log(" Raising sheep ");
	console.log(" Feed the horse ");
	console.log(" Kindling wood ");
	console.log(" eagle ");
}
//js Call directly 
fun();
// stay dom1 Event call 
var btn = document.querySelector("button");
btn.onclick = fun;

3、 ... and 、 The parameters of the function

• parameter list ： Function has a very special variable arguments, An array like variable storage function passes in a parameter list
• Formal parameters can be used at will , Just be consistent

function say(name){
	alert(" I like it "+name)
}
say(" Apple ");
say(" Xiao Tong ");

Four 、 Multiple parameters

function add(a,b){
	var sum = 0;
	for(var i=a;i<=b;i++){
		sum+=i;
	}
	alert(sum);
}
add(2,5);

5、 ... and 、 Function default parameters

function send(name="rose"){
	alert(` dear ${name}, I miss you `);
}
send(" Xiao Tong ");
send();
send(" floret ");
send();

6、 ... and 、 The return value of the function

• Function returns... By default undefined
• use return Keyword can define the function return value
• return Later code Function does not execute

function add(a,b){
	return a+b;
	alert(a+b);
}
var re = add(3,4);
console.log(re);

7、 ... and 、 Anonymous functions

• Functions without names
• Register at event ：el.onclick = function(){}
• As a callback function ：list.forEach(function(item){})
• Anonymous function self executing ：(function(){...})
• Assign a value to a variable and declare it before executing ：var abc =function(){...}

//1. Bound with events 
var h1 = document.querySelector("h1");
h1.onclick = function(){
	alert(" Hello ");
}

//2. As a callback function 
var ps = document.querySelectorAll("p");
ps.forEach(function(item){
	console.log(item.innerText)
});

//3. Self execution 
(function(){alert(" I like you ")})()
!function(){alert(" I don't like you ")}()

8、 ... and 、 Scope

Global scope ：

• stay js You can visit anywhere
• stay script use var Declared variables
• window The global properties of
• Variables that are not declared with keywords anywhere are also global variables

Function scope ：

• In the current function , Subfunctions can access
• Variables declared in the current function
• Function can access its parent element scope / Global scope variables cannot access function internal variables outside the function
• if,switch,else,for No scope

var a =15;
function say(){
	var b =5;
	function son(){
		alert(a+b);
	}
	son();
}
say();
alert(b);