Analysis on the concepts and usage of JS anonymous functions and anonymous self-executing functions

This article mainly introduces the concepts and usage of JS anonymous functions and anonymous self-executing functions. It analyzes the concepts, functions, application scenarios and related usage skills of anonymous functions and anonymous self-executing functions in the form of examples. Friends in need can refer to it. Next

The examples in this article describe the concepts and usage of JS anonymous functions and anonymous self-executing functions. Share it with everyone for your reference, the details are as follows:

1. Common scenarios of anonymous functions

The anonymous function in js is a very common function type, compare Common scenarios:

<input type="button" value="点击" id="btn">
<script type="text/javascript">
  //匿名函数的第一种情形
  var btn=document.querySelector("#btn");
  btn.onclick=function(){
    // alert("aaaaa");
  }
  //匿名函数的第二种情形
  setInterval(function(){
    // alert("bbbbb");
  }, 1000);
  //匿名函数的第三种情形
  var fun=function(){
    alert("ccccc");
  }
  // fun();
  //匿名函数的第四种情形
  var obj={
    name:"dddd",
    say:function(){
      alert(this.name);
    }
  }
  obj.say();
</script>

The above shows the common usage scenarios of anonymous functions. (Note: querySelector is a new method of finding DOM elements in H5)

2. Anonymous self-executing function

As the name suggests, anonymous self-executing function first It is an anonymous function, but this function can be executed automatically by itself without the help of other elements.

<input type="button" value="点击" id="btn">
<script type="text/javascript">
//1，匿名函数的第一种实现方式
(function(data){
  // alert(data);
})("eee");
//2.匿名自执行函数的第二种实现方式
(function(){
  // alert("fff");
}());
//3.匿名自执行函数的第三种实现方式
!function(data){
  // alert(data);
}("hhh");
//4.匿名自执行函数的第四种实现方式
var fun=function(data){
  alert(data);
}("iii");

From the above code block, we can summarize that there are generally four methods to implement anonymous self-executing functions.

3. The role of anonymous self-executing functions

①. The most common role of anonymous self-executing functions is to implement closures. I will introduce the concept of closure in detail in a later article. Here is a brief explanation of closures. Closure: Closure is a feature of js. We can use closure to realize the connection inside and outside the function, and can make the local variables of the function always exist in the memory.

②. Anonymous self-executing functions can also be used to simulate the creation of block-level scopes in js, that is, If you use anonymous self-executing functions to wrap some code, you can achieve block-level effects. The effect of the domain is to reduce the number of global variables. After the execution of the anonymous self-executing function is completed, the variables will be released from the memory, thus saving memory.

4. Summary of anonymous functions and anonymous self-executing functions

Anonymous functions can be simply understood as functions without names. There are 4 common scenarios in total. .

Anonymous self-executing functions can be simply understood as anonymous functions that can be executed by themselves. There are four ways to implement anonymous self-executing functions.

The purpose of anonymous self-executing functions is to use closures and create independent namespaces.

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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