Pattern & Problem Description

This seems way trivial, but never the less I am going to pose because I cannot find a simple clear example. Note if you respond with a function and do not declare a class then I will not accept that as a solution. I do understand that JS considers classes to function...

1. I define a class

class MyClass{
    constructor(input0){
        this._input0 = input0;
        this._input1 = [];
    }
    set_input1(){
        /**
         * in my case complex algebraic manipulation occurs inside this function
         * by putting it inside of a function it encapsulates that
         * in this the result is 123 ;)
         */
         this._input1.push(123);
    }

Now to actually initialize the object as shown here. In this case input0 is set to 'foo'

myobj = new MyClass('foo')
myobj.set_input1()
console.log(myobj._input1)  //returns empty array []

TODAY'S EXAMPLE

Today I was building a data aggregator with nodejs and could not get this to go.

ProjDb.js

class ProjDb {
    constructor(_rsviewProjDirArr) {
        this._rsviewProjDirArr = _rsviewProjDirArr;  // Full file directory paths
        this._allFileNameArr = [];
   }   // end constructor
    set_allFileNameArr() {
        this._rsviewProjDirArr.forEach((i) => {
            fs.readdir(i, (err, files) => {
                if (err) {
                    throw (err);
                }
                else {
                    files.forEach(file => {
                        if (path.extname(file) == ".DBF") {
                            this._allFileNameArr.push(file);
                        }
                    });
                }
            });
        });
    }
}// end classs = ProjDb

module.exports = ProjDb;

SERVER.js

const XLSX = require('xlsx');
const util = require('util');
const ProjDb = require('./ProjDb.js');

let projDb = new ProjDb(
    ['./rsview-data/proj1',
     './rsview-data/proj2']);


projDb.set_allFileNameArr();
console.log(projDb._allFileNameArr.length);  // result =0 but should be large number

I like this pattern because debugging is very easy on small devices and complex systems. I can break out the problem quickly. It also makes code easy to read. The only thing I have been able to come up with is that because there is a scope wrapping the constructor I cannot redefine the values inside of it...I do this all the time in cpp, and python. So if you can explain from that perspective I would love it. I don't see either of these should fail.

CodePudding user response：

in the constructor you have this._input1 = [];

however the console is console.log(myobj.input1)

works fine if you fix the name typo:

class MyClass{
    constructor(input0){
        this._input0 = input0;
        this._input1 = [];
    }
    set_input1(){
        /**
         * in my case complex algebraic manipulation occurs inside this function
         * by putting it inside of a function it encapsulates that
         * in this the result is 123 ;)
         */
         this._input1.push(123);
    }
}

myobj = new MyClass('foo')
myobj.set_input1()
console.log(myobj._input1)  // [123]

CodePudding user response：

After some digging, I found a way. It appears that you can update the member function as one would expect. The **code in the second example is using node function from fs module fs.readdir. After a review, I found that the files is a keyword for the callback and must be used, additionally it returns an object not an array. So that object must be transformed into a string array using the built-in toString() member.

here is the working copy

set_allFileNameArr() {
        // rename i as dirpath
        
        for (let i=0;i<this._rsviewProjDirArr.length;i  )
        {
            let _dirPath = this._rsviewProjDirArr[i];
            var logstream = fs.createWriteStream('allFileNameArr.txt', {flas: 'a'});
            
            console.log('Loading Data From Target Directory:\n\t' _dirPath)
            // Method 1
            // (err,files) are 2 arguments for a callbqack function 
            fs.readdir(_dirPath, (err, _files)=>{
                if (err) throw (err);
                else {
                    // For loop style
                    for (let i=0;i<_files.length;i  ){
                        if(path.extname(_files[i])==='.DBF'){
                            this._allFileNameArr.push(_files[i].toString()); 
                            logstream.write(_files[i].toString() '\n')
                            
                        }
                    }
                }
            }
            );