Sharing the concepts and usage of JS anonymous functions

This article mainly introduces the concepts and usage of JS anonymous functions and anonymous self-executing functions, and analyzes the concepts, functions, application scenarios and related usage skills of anonymous functions and anonymous self-executing functions in the form of examples. I hope it can help everyone. .

1. Common scenarios of anonymous functions

The anonymous function in js is a very common function type, and the more common scenarios are:

<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 ways 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 role of anonymous self-executing functions is to use closures and create independent namespaces.

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