Example analysis of js recursion and timer

This article mainly introduces the relevant knowledge of js recursion and timer. It has a very good reference value. Let’s take a look at it with the editor.

Recursion: It is formed by a function calling itself;

First of all An example:

Function factorial(num){
 if(num<=1){
 return 1;
 }else{
 return num*factorial(num-1);
 }
}

This is a classic recursive factorial function, but some errors may occur when calling it in js: For example, the following code

var anotherFactorial = factorial;
factorial = null;
alert(anotherFactorial)// 出错

The above code first saves the factorial() function in the variable anotherFactorial, and then sets the factorial variable to null. As a result, there is only one reference to the original function. But when anotherFactioral() is called next, because the factorial function must be executed, and factoial is no longer a function, an error will occur. In this case, using arguments.callee can solve this problem.

arguments.callee is a pointer to the function being executed, so it can be used to implement recursive calls to the function.

For example:

function factorial (num){
 if(num){
 return 1;
 }else{
 return num*arguments.callee;
 }
}

##arguments.callee Advantages:

1. It can ensure that no problem will occur no matter how the function is called. Therefore, when writing a recursive function, it is safer to use arguments.callee than to use the function name;

Note: It is invalid in strict mode and an error will be reported

var factorial = (function f(){
 if(num<1){
 return 1;
 }else{
 return num*f(num-1);
 }
})

JS is a single-threaded language, but it allows scheduling code to be executed at specific moments by setting timeout calls and intermittent times. The former executes the code after a specified time, while the latter executes the code every specified time.

Parameters: the code to be executed and the time in milliseconds

//不建议传字符串,传递字符串可能导致性能损失 
setTimeout("alter('hello word')", 1000);
//推荐方式
setTimeout(function(){
 alter("Hello world");
},1000)
setInterval(function(){
 alter("Hello world");
},1000)

Note: End

The code called with timeout is executed in the global scope, so the value of this in the function points to the window object in non-strict mode, and is undefined in strict mode; Actual In application:

Using timeout calls to simulate intermittent calls is the best mode. In a development environment, real intermittent calls are rarely used because the latter intermittent call may Started between previous intermittent calls.

var num = 0, max = 0;
function incrrmentNumber{
 num++;
 if(num < max){
 setTimeout(incrrmentNumber,500);
 }else{
 alert("Done");
 }
}
setTimeout(incrrmentNumber,500);

You can avoid this if you use a timeout call like above. So don’t use intermittent calls;

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