const axios = require('axios');
const request = require('request');
/*
    issue with this approach:
        - nested: bad design, no limit of how many levels functions can be nested, arguments from callback(err, body) have to
        renamed constantly to prevent overlap
        - readability: not very readable, may need to nest multiple times
        - usability: as a provider of functions, need to maintain callback as last argument
*/
//request.get('http://google.com.sg',{query :{ name: "hello"}}, (err, body)=>{
request.get('http://google.com.sg', (err, body)=>{
    if(err){
        console.log("do something with error");
        return;
    }
    console.log("do something with data");
    request.get('http://youtube.com.sg', (err2, body)=>{
        if(err2){
            console.log("do something with error nested");
            return;
        }
        console.log("do something with data nested");
    })
});
/*
Promises explained as callbacks:
    - if err is null , the function passed to "then" will be called(successful)
    - if err is not null, the function passed to "catch" will be called(error)
Benefits:
    - although then and catch accepts a function, as promises are returned and not defined in how u call the function(referring to callbacks),
      you can just return another function which returns a function
    - err and body are separated, do not need to have ugly syntax of line 11 - 14, what to do when successful and error are clearly defined and seperated
    - no need to maintain rule of having callback last argument to function
*/
/*axios.get("http://google.com.sg",{
    query: {
        name: "hello"
    }
})*/
axios.get("http://google.com.sg").then((body)=>{
    console.log("do something with data");
    return axios.get("http://youtube.com.sg");
}).catch((err)=>{
    console.log("do something with error");
}).then((body)=>{
    console.log("do something with data another then");
}).catch((err)=>{
    console.log("do something with error");
});