Callback Function -> Golang & NodeJS

 

Callback: Passing a Function as an Argument
                   GoLang Example
 Supper Example 1:

       https://play.golang.org/p/AI8jKiYIKO6

 Supper Example 2:

• Supper Example 3:

package main

import "fmt"

func visit(numbers []int, callback func(int)) {
   for _, n := range numbers {
      callback(n)
   }
}

func main() {
   visit([]int{1, 2, 3, 4}, func(n int) {
      fmt.Println(n)
   })
}

// callback: passing a func as an argument

package main

import "fmt"

func filter(numbers []int, callback func(int) bool) []int {
   var xs []int
   for _, n := range numbers {
      if callback(n) {
         xs = append(xs, n)
      }
   }
   return xs
}

func main() {
   xs := filter([]int{1, 2, 3, 4}, func(n int) bool {
      return n > 1
   })
   fmt.Println(xs) // [2 3 4]
}

package main

import (
   "fmt"
)

func main() {
   ii := []int{1, 2, 3, 4, 5, 6, 7, 8, 9}
   s := sum(ii...)
   fmt.Println("all numbers", s)

   s2 := even(sum, ii...)
   fmt.Println("even numbers", s2)

   s3 := odd(sum, ii...)
   fmt.Println("odd numbers", s3)
}

func sum(xi ...int) int {
   total := 0
   for _, v := range xi {
      total += v
   }
   return total
}

func even(f func(xi ...int) int, vi ...int) int {
   var yi []int
   for _, v := range vi {
      if v%2 == 0 {
         yi = append(yi, v)
      }
   }
   return f(yi...)
}


func odd(f func(xi ...int) int, vi ...int) int {
   var yi []int
   for _, v := range vi {
      if v%2 != 0 {
         yi = append(yi, v)
      }
   }
   return f(yi...)
}

NodeJS Example

var express = require('express');
var app = express();
var fs = require("fs");

var user = {
   "user4" : {
      "name" : "mohit",
      "password" : "password4",
      "profession" : "teacher",
      "id": 4
   }
}

app.post('/addUser', function (req, res) {
   // First read existing users.
   fs.readFile( __dirname + "/" + "users.json", 'utf8', function (err, data) {
      data = JSON.parse( data );
      data["user4"] = user["user4"];
      console.log( data );
      res.end( JSON.stringify(data));
   });
})

var server = app.listen(8081, function () {
   var host = server.address().address
   var port = server.address().port
   console.log("Example app listening at http://%s:%s", host, port)

https://www.tutorialspoint.com/nodejs/nodejs_restful_api.htm