Analyze the conceptual understanding and usage of javascript callback functions

This article mainly introduces the conceptual understanding and usage of javascript callback functions. It analyzes the functions, principles, usage methods and related precautions of javascript callback functions based on specific examples. Friends in need can refer to it

The examples in this article describe the conceptual understanding and usage of javascript callback functions. Share it with everyone for your reference, the details are as follows:

1. The role of the callback function

js code will be executed from the top to the next line, but sometimes we need Wait until one operation is completed before proceeding with the next operation. At this time, you need to use the callback function.

2. Explanation of callback function

Because a function is actually an object, it can be stored in a variable and passed to another function through parameters. In the function Created internally, return the result value from the function", because the function is a built-in object, we can pass it as a parameter to another function, execute it in the function, and even return it after execution, it has always been used by "professional programmers" Seen as a difficult technology, the English explanation of

is:

A callback is a function that is passed as an argument to another function and is executed after Its parent function has completed.

Translation is: the callback function is a function passed as a variable to another function, which is executed after the main function is executed.

function A. There is a parameter function B. Function B will be called and executed after function A is completed.

3. How to use the callback function

The code is as follows:

function a(callbackFunction){
  alert("这是parent函数a");
  var m =1;
  var n=3;
 return callbackFunction(m,n);
}
function b(m,n){
  alert("这是回调函数B");
  return m+n;
}
$(function(){
  var result = a(b);
  alert("result = "+ result);
});

The execution sequence is:

这是parent函数a
这是回调函数B
result = 4

The function first executes the theme function a, and then calls Callback function b, and finally return the return value of function a

.

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