Original blog ：https://blog.csdn.net/yaojxing/article/details/72784774

1. Common scenarios for anonymous functions

js Anonymous functions in are a very common type of functions , More common scenarios :

  1. <input type="button" value=" Click on " id="btn">
  2. <script type="text/javascript">
  3. // The first case of anonymous functions
  4. var btn=document.querySelector("#btn");
  5. btn.onclick=function(){
  6. // alert("aaaaa");
  7. }
  8. // The second case of anonymous functions
  9. setInterval(function(){
  10. // alert("bbbbb");
  11. }, 1000);
  12. // The third case of anonymous functions
  13. var fun=function(){
  14. alert("ccccc");
  15. }
  16. // fun();
  17. // The fourth case of anonymous function
  18. var obj={
  19. name:"dddd",
  20. say:function(){
  21. alert(this.name);
  22. }
  23. }
  24. obj.say();
  25. </script>

The above shows the common use scenarios of anonymous functions .( Be careful :querySelector yes H5 New search in dom Element method )

2. Anonymous self executing function

See the name, think of the meaning , An anonymous self executing function is, first of all, an anonymous function , But this function is self executing , No need for other elements .
  1. <input type="button" value=" Click on " id="btn">
  2. lt;script type="text/javascript">
  3. //1, The first way to implement anonymous functions
  4. (function(data){
  5. // alert(data);
  6. })("eee");
  7. //2. The second implementation of anonymous self executing function
  8. (function(){
  9. // alert("fff");
  10. }());
  11. //3. The third way to implement anonymous self executing functions
  12. !function(data){
  13. // alert(data);
  14. }("hhh");
  15. //4. The fourth way to implement anonymous self executing functions
  16. var fun=function(data){
  17. alert(data);
  18. }("iii");
From the above code block, we can conclude that there are four ways to implement anonymous self executing functions .

3. The role of anonymous self executing functions

1. The most common use of anonymous self executing functions is in the case of closures . I'll explain the concept of closure in detail in the following blog . Here's a brief description of closures . Closure : Closure is js A characteristic of , We can connect the inside and outside of a function through closures , And it can make the local variables of function always exist in memory .
 
2. Anonymous self executing functions can also be used in js Create a block level scope in the simulation , That is, if you use anonymous self executing functions to wrap some code, you can achieve the effect of block level scope , Reduce the number of global variables , After the anonymous self executing function is executed, the variable will be released by memory , And that saves memory .
 

4, Summary of anonymous functions and anonymous self executing functions

Anonymous functions can be simply understood as functions without names , The common scenes are 4 Kind of .
Anonymous self executing functions can be simply understood as anonymous functions that can be executed by themselves , There are several ways to implement anonymous self executing functions 4 Kind of .
The function of anonymous self executing function is used for closure and creating independent namespace .

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