Callback functions are used in asynchronous programming to perform certain tasks after a main function has finished executing. They are commonly used in JavaScript and NodeJS. Here is a simple example on how to implement a callback function.
1. Define a function that will do the main operation.
```
function mainFunction(input, callback) {
// Some operations on input
let result = input*2;
In this function, the `callback` parameter is a function. After `result` is computed, the callback function is called with `result` as its parameter.
1. Define a callback function that will be called after the main function.
```
function callbackFunction(result) {
// Print the result
console.log(‘The result is ‘ + result);
}
```
1. Call the main function with the callback function as its second parameter.
```
mainFunction(5, callbackFunction);
```
After running `mainFunction`, `callbackFunction` will be called, which will print: “The result is 10”.
Note: Callback functions should be used carefully to avoid “callback hell”, where code becomes deeply nested and difficult to read. For managing complex asynchronous code, consider using Promises or async/await.
