What is an infinite loop in web front-end

An infinite loop refers to a loop that cannot be terminated by its own control. It is a phenomenon in which a single program continues to perform loop operations in a certain link because the conditions for breaking out of the loop are not met. An infinite loop can bring the program to a standstill, and in severe cases can slow down the computer. It is one of the most troublesome malfunctions for programmers.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

Looping is to do one thing repeatedly. In the process of writing code, we often encounter some operations that need to be performed repeatedly, such as traversing some data, repeatedly outputting a certain string, etc. If one line of It would be too troublesome to write. For this kind of repeated operation, we should choose to use a loop to complete it.

The purpose of a loop is to repeatedly execute a certain piece of code. Using loops can reduce programming pressure, avoid code redundancy, improve development efficiency, and facilitate later maintenance.

var i = 11;
do{
  document.write(i++ +"<br />");
}while(i <= 10);

while(true){
  alert(1);
}

You can repeatedly execute a piece of code multiple times through a loop statement

What is an infinite loop

The meaning of "infinite loop": the phenomenon of continuous loop operation in a single program because the conditions for breaking out of the loop are not met in a certain link. It refers to a loop that cannot be terminated by its own control. In programming, a program that cannot be terminated under its own control.

The "infinite loop" can bring the program to a standstill. In severe cases, it can slow down the computer. It is one of the fault conditions that gives programmers a headache.

var n = 1;
while(true){
  alert(n++);
  
  //判断n是否是10
  if(n == 10){
    //退出循环
    break;
  }  
}

A loop like this where the conditional expression is written to true is called an infinite loop

The loop will not stop unless the browser is closed, infinite loops should be used with caution in development

You can use break to terminate the loop

Extended knowledge: Commonly used loop statements in the web front-end

1. while loop

##1.1. Syntax:

while(条件表达式){ 
  语句...
}

1.2. Execution process

• When the while statement is executed, the conditional expression is first evaluated and judged
  If the value is true, the loop body is executed
• After the execution of the loop body is completed, continue to judge the expression
  If it is true, continue to execute the loop body, and so on
  • If the value is false, terminate the loop

##2. do...while loop

2.1. Syntax:

do{   
  语句。。。
}while(条件表达式)

2.2. Execution process

When the do...while statement is executed, the loop body will be executed first
After the loop body is executed, the conditional expression after the while will be judged

• If the result is true, continue to execute the loop body, continue to judge after execution, and so on
  • If the result is false, terminate the loop

3. Comparison between while and do...while

In fact, the functions of these two statements Similarly, in different formats, while is judged first and then executed

• , while do...while is executed first and then judged
do...while can guarantee a loop. The body is executed at least once

• but while cannot be

##4 . for loop

//创建一个执行10次的while循环
//初始化表达式
/* var i = 0;

//创建一个循环，定义条件表达式
while(i < 10){
	//设置更新表达式
	alert(i++);
} */

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

##4.1. Description

The for statement is also a loop statement, also called a for loop

• In the for loop, we are provided with a special location for placing Three expressions:

• Initialization expression
  Conditional expression
  • Update expression

4.2. Syntax of for loop:

for(①初始化表达式;②条件表达式;④更新表达式){
  ③语句...
}

##4.3. Execution process

//创建一个循环，定义初始化表达式和条件表达式
while(var i = 0;i < 10){
	//设置更新表达式
	alert(i++);
}

①Execute the initialization expression and initialize the variables (the initialization execution expression will only be executed once)

• ②Execute the conditional expression to determine whether to execute the loop

If it is true, execute the loop

• If it is false, terminate the loop

  • ##④Execute the update expression, and continue to repeat after the update expression is executed ②

• ##4.4. Supplementary abbreviation

All three parts in the for loop are acceptable If omitted, it can also be written in external

如果在for循环中不写任何的表达式，只写两个;

此时的循环是一个死循环会一直执行下去，慎用

for(;;;){
	alert("hello");
}

（学习视频分享：web前端入门）

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