JS for while loop

This time I will bring you the for while loop of JS, what are the precautions for using the for while loop of JS, the following is a practical case, let's take a look.

Loop statement:

For

##　for loop format

for（var i = 0; i < 10;  i ++）{   }

For loop execution sequence:

Enter ② Judgment... Loop

If the judgment is false, end

while

　

while loopFormat

var i = 0;
while（i < 10）{ 
    alert();
    i ++;    break;
}

If i<10 is replaced with true, the while loop will continue to execute. until the conditional control ends.

break ends all loops

continue skips this loop and will execute the following.

for（）{
     If（i ==2）{
        Continue;
    }                            
}

View Code

will skip the case of i=2, end i=1 and then execute i=3.

The difference between for and while

To determine the number of times, use for

While while terminates the loop until a certain condition is met. (Looking for books in the library, I don’t know how many books)

Variable classification:

1. Global variables are also called external variables, which are variables defined outside the function. It does not belong to a function, it belongs to a source program file. Its scope is the entire source program.

2. Local variables In a program, variables that can only be accessed in a specific procedure or function are relative to global variables

Scope:

The scope of the variable Only within defined curly braces.

Short circuit:

Only performs one operation, high efficiency

Other content:

　

Typeof

DetermineData type There is a return value                                           # (Can you assign a value to a variable?) Var num = 1+2 && 3+4 Output 3 is judged to be true because both sides are true

　0 false　Not 0 true

Empty false

Non-empty true

##Notes

：

Homework questions:

Control statementNote the format

if(判断){
    alert();
}else{
    alert();
}

if语句格式

　　　　变量要在开头定义。

　　　　重复的代码要优化重构。

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