What are the javascript conditional control statements?

js conditional control statements include: 1. if statement; 2. "if... else if... else..." statement; 3. switch statement; 4. while statement; 5. "do...while" statement; 6 , for statement; 7. "for...in" statement; 8. with statement.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

if statement:

var box=50;
if (box == 50){
	alert("True');
}

if … else if … else…

var box = 50;
if (box > 0 && box <60){
	alert("不及格");
}else if (box >=60 && box < 80){
	alert("及格");
}else if (box >= 80 && box <= 100){
	alert("good");
}else{
	alert("数值错误");
}

switch statement is a multiple conditional judgment, used for comparison of multiple equal values.

var box = 4;
switch (box){
     case 1:
         alert("one");
         break;
     case 2:
         alert("two");
         break;
     case 3:
         alert("three");
         break;
     default:
         alert("默认值");
         break;
 }						// 由于case没有可以匹配到4的项，所以使用default中的内容

The while statement is a kind of statement that is judged first and then looped. The condition must be met before the loop body will be executed.

var box = 5;
while(box > 0){
	alert(box);
	box--;
};

do...while statement is a kind of loop that is executed first and then judged. statement, that is to say, regardless of whether the condition is met, it will be executed at least once in the loop body

var box = 1;
do{
	alert(box);
	box++;
}while (box < 5);

The for statement is also a statement that judges first and then loops, but it can initialize the variables before the loop

for (var box=1; box<=5; box++){			//第一步，声明变量 var box = 1;
	alert(box);				// 第二步，判断box <=5;	
	};					// 第三步，执行循环体内alert(box);
						// 第四步，box++
						// 第五步，从第二步开始再次判断执行，直到判断为false停止循环。

# The ##for…in statement is a precise iteration statement that can be used to enumerate the properties of an object.

var list = [1, 2, 3, 4, 5];
for (var i in list){
	document.write(i);	//迭代的是数组的下标
};				
var p = {name: "张三", age:18, sex: "男"}; // 创建一个对象，键值对，冒号左边是属性名，右边是值
for (var i in p){
	console.log(i, p[i]);	// 列举出所有的属性和值，循环列举出p，每个i就是p的每个属性名，p[i]就是p[属性名]，比如p[name]可以显示出属性为name的那个值。
};

The function of the with statement is to set the scope of the code to a specific object.

var box = {
	name: "张三",
	age: 18,
	sex: ”男",
};
/*从对象里取值赋给变量*/
var a = box.name;
var b = box.age;
var c = box.sex;

/*可以将上面三段的赋值操作改为：*/
with (box){
	var a = name;
	var b = age;
	var c = sex;
}					// 省略了box的对象名

DOM(Document Object Model) Document Object Model

Node(Node)

When loading an HTML page, the web browser generates a tree structure to represent the page internal structure. DOM understands this tree structure as consisting of nodes

#Node types: element nodes, text nodes, attribute nodes.

<div title="属性节点">测试 Div</div>

[Recommended learning:

javascript advanced tutorial]

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