I am trying one logic in Node JS code which looks something like below:-
var startPersons1 = JSON.parse(JSON.stringify(persons1));
var startPersons2 = JSON.parse(JSON.stringify(persons2));
var startPersons3 = JSON.parse(JSON.stringify(persons3));
var startPersons4 = JSON.parse(JSON.stringify(persons4));
.....
// Operations on persons1, persons2, persons3, persons4 which are changed in methods called here
....
// Now persons1, persons2, persons3, persons4 are modified
// Now, if I wanted persons1, persons2, persons3, persons4 to come to their original state above, ie.
// startPersons1, startPersons2, startPersons3, startPersons4, I am doing something like this
persons1 = JSON.parse(JSON.stringify(startPersons1));
persons2 = JSON.parse(JSON.stringify(startPersons2));
persons3 = JSON.parse(JSON.stringify(startPersons3));
persons4 = JSON.parse(JSON.stringify(startPersons4));
You can assume this is inside some for loop.
So, is there a better way to do this revert everytime. The number of variables can increase by lot.
if persons1, persons2 etc are inside an array, you could use map function
var persons = [/*array of persons*/]
var newpersons = persons.map(function(person) {
/*change here your person object and return it.*/
return person
})
/*here persons is the originalone, newpersone is the new version*/
Related
I have a function which returns an array of dishes from a firestore database.
With console.log I check that the dish I want to push is correctly formatted, then push it.
Finally I console.log the array to check if everything is alright.
Here is what I got:
https://image.noelshack.com/fichiers/2019/05/5/1549048418-arraypush.png
switch (type) {
case "Plats": {
this.nourritureCollection.ref.get().then(data => {
let platArray : Plat[] = [];
data.docs.forEach(doc => {
this.plat.name = doc.data().nourritureJson.name;
this.plat.price = doc.data().nourritureJson.price;
this.plat.ingredients = doc.data().nourritureJson.ingredients;
this.plat.type = doc.data().nourritureJson.type;
this.plat.availableQuantity = doc.data().nourritureJson.availableQuantity;
this.plat.isAvailableOffMenu = doc.data().nourritureJson.isAvailableOffMenu;
this.plat.imgUrl = doc.data().nourritureJson.imgUrl;
this.plat.temp = doc.data().nourritureJson.temp;
console.log(this.plat)
platArray.push(this.plat);
});
console.log(platArray)
return platArray;
});
break;
}...
plat is instantiated within my service component, I couldn't declare a new Plat() inside my function.
The expected result is that dishes should be different in my array of dishes.
You are updating this.plat in every iteration. So it will have n number of references in the array pointing to the same object, therefore, the values for all the array elements will be last updated value of this.plat
What you need is to create new Plat object for every iteration.
data.docs.forEach(doc => {
let plat: Plat = new Plat();
plat.name = doc.data().nourritureJson.name;
plat.price = doc.data().nourritureJson.price;
plat.ingredients = doc.data().nourritureJson.ingredients;
plat.type = doc.data().nourritureJson.type;
plat.availableQuantity = doc.data().nourritureJson.availableQuantity;
plat.isAvailableOffMenu = doc.data().nourritureJson.isAvailableOffMenu;
plat.imgUrl = doc.data().nourritureJson.imgUrl;
plat.temp = doc.data().nourritureJson.temp;
console.log(plat)
platArray.push(plat);
});
As pointed out in the comment, you can only use new Plat() if Plat is a class, if it is an interface, just let plat:Plat; would do.
I'm using SQLite with sql.js on my project and I have been having some trouble with my implementation. Seems like the queries are being run on the database twice because for the for the INSERT statements I get 2 records in the DB.
The way I do it, I create the SQL and then pass it on to this method (the opts variable contains all of the data being put into the database):
prepareStatementAndCompileResults(db, sql, opts){
const stmt = db.prepare(sql);
const result = stmt.getAsObject(opts);
var rows = [];
if(!this.isEmpty(result)){ // isEmpty is a simple method that checks for empty objects
rows.push(result);
}
while(stmt.step()) {
var row = stmt.getAsObject();
rows.push(row);
}
this.saveToFile(db);
stmt.free();
return rows;
},
Here is a sample SQL INSERT that is being run twice
INSERT OR IGNORE INTO tag_event (tag_id, event_id, unique_string)
VALUES (:tag_id,:event_id, :unique);
Here is what the opts variable would look like for this query:
var opts = {
[':tag_id']: 1,
[':event_id']:1,
[':unique']: '1-1'
}
Because you're pushing it into row 2 time.
// if not empty will add to row
if(!this.isEmpty(result)){ // isEmpty is a simple method that checks for empty objects
rows.push(result);
}
// not sure what step() does but I'm assuming this will also run
while(stmt.step()) {
var row = stmt.getAsObject();
rows.push(row);
}
Verify by using a debugger or just console.log(rows) after the while loop before the save
So, what it turns out I needed to do was bind the variables to the prepared statement before getting the rather than binding them through getAsObject. This is much more efficient. My API response time on a local test went from 785ms to 14.5ms
prepareStatementAndCompileResults(db, sql, opts){
const rows = [];
const stmt = db.prepare(sql);
stmt.bind(opts);
while(stmt.step()) {
var row = stmt.getAsObject();
rows.push(row);
}
this.saveToFile(db);
stmt.free();
return rows;
},
I want to create an object dynamically in node. To do that i used a code like this.
Is this use of eval in a node server a bad idea?
var a1 = require(./a1.js),
a2 = require(./a2.js),
...
aN = require(./aN.js);
function createObj(pObjName, pObjValue){
var tmp = new eval(pObjName)(pObjValue);
//where pObjName is a1 or a1 or .... or aN
}
From what you're showing, there's no need to use eval:
const Classes = {
a1 : require('./a1'),
a2 : require('./a2'),
...
};
function createObj(pObjName, pObjValue){
var tmp = new Classes[pObjName](pObjValue);
...
}
Seems like you want to create objects with a set of properties?
You might want to look at the Object.create()-method
If you want to save yourself the time of declaring all of those dependencies, you could even write a function without using eval that handles the case even more efficiently:
function createObj(pObjName, pObjValue) {
var tmp = new (require('./' + pObjName))(pObjValue);
// ...
}
Please note that this is only safe if createObj() is guaranteed to be invoked with a pObjName that is what you expect, otherwise you'll need to validate it first, possibly something like this:
function createObj(pObjName, pObjValue) {
if (!/^a\d$/.test(pObjName)) {
throw new TypeError('invalid name')
}
var tmp = new (require('./' + pObjName))(pObjValue);
// ...
}
I have a ES6 class in NodeJS 4 :
vehicule.js
"use strict";
class Vehicule {
constructor(color) {
this.color = color;
}
}
module.exports = Vehicule;
When I need to instanciate in another file, I find myself doing this :
var _Vehicule = require("./vehicule.js");
var Vehicule = new _Vehicule();
I'm new to nodeJs, is there a way to do this in one line, or at least in a more readable way ?
A class is really supposed to be reused for many objects. So you should require the class itself:
var Vehicule = require("./vehicule.js");
and then create objects from it:
var vehicle1 = new Vehicule('some data here');
var vehicle2 = new Vehicule('other data here');
Usually classes start with an upper case letter, and instances of classes (objects themselves) with a lower case one.
If you want a "class" for just one objects, you can just create an inline object:
var vehicle = {
myProperty: 'something'
};
module.exports = vehicle;
//in some other file
var vehicle = require('vehicle');
Though if you really, really want to do that in one line, you can do:
var vehicle = new (require('vehicle'))('some constructor data here');
But that is not recommended. Pretty much ever.
If you really want to do this in one line:
var Vehicule = new (require('./vehicule'))('red');
but personally i would prefer two lines for the same reasons mentioned by #ralh.
main.js
var count = 1;
// psuedocode
// if (words typed begins with #add)
require('./add.js');
// if (words typed begins with #remove)
require('./remove.js');
// if (words typed begins with #total)
require('./total.js');
module.exports.count = count;
total.js
var count = require('./main.js').count;
console.log(count);
add.js
var count = require('./main.js').count;
count += 10;
console.log(count);
remove.js
var count = require('./main.js').count;
count -= 10;
console.log(count);
console.log
1
11
-9
Background:
I have an application (irc bot), and I want to add a feature that peeps can do #add 1 or #remove 1. I have a main.js that then requires different files depending on the triggers that are said. So add would trigger the add.js file, and that would then require('main.js') and add 10 (10 for simplification, it'll actually parse the number and use that number) to it. The problem I'm having is when someone goes about and does #remove. It require('main.js') and subtracts 10 from 1 resulting in -9. And doing #total would output 1.
I've done a fairly good search for module.exports and I haven't come across an example like the one i listed above. The docs don't include any examples close to what I'm wanting to do; and these questions 1, 2 I understand--but aren't of any usefulness to me--as I understand what's being said there.
Question:
I'd like to have both #add and #remove manipulate the same variable ( count ), and for #total to return the total of count with the #add and #removes taken into account. Am I using module.exports incorrectly; or is there a common way that variables are shared, with one file being able to modify the contents of the module.exports and returning the results to the main.js file?
Your problem is that when you do var count = require('./main.js').count;, you get a copy of that number, not a reference. Changing count does not change the "source".
However, you should have the files export functions. Requiring a file will only run it the first time, but after that it's cached and does not re-run. see docs
Suggestion #1:
// main.js
var count = 1;
var add = require('./add.js');
count = add(count);
// add.js
module.exports = function add(count) {
return count+10;
}
#2:
var count = 1;
var add = function() {
count += 10;
}
add();
#3: Personally i would create a counter module (this is a single instance, but you can easily make it a "class"):
// main.js
var counter = require('./counter.js');
counter.add();
console.log(counter.count);
// counter.js
var Counter = module.exports = {
count: 1,
add: function() {
Counter.count += 10;
},
remove: function() {
Counter.count += 10;
}
}
Not sure if this new or not but you can indeed share variables between files as such:
main.js
exports.main = {
facebook: null
};
counter.js
var jamie = require('./main');
console.info(jamie); //{facebook: null}
jamie.main.facebook = false;
console.info(jamie); //{facebook: false}
anothercheck.js
var jamie = require('./main');
console.info(jamie); //{facebook: null} //values aren't updated when importing from the same file.
jamie.main.facebook = true;
console.info(jamie); //{facebook: true}
Now you can share between files.
I know I'm a little bit late to answer this questions, just 7yrs!
You can simply use a global variable:
global.myVar = 'my-val';
console.log(myVar); // returns 'my-val'
// from here on it's accessable to all modules by just the variable name
using-global-variables-in-node-js
I have same problem like you,.. Sometimes I'd like to sharing variables between multiple files because I love modular style eg. separating controller, function, models in different folders/files on my node.js script so I can easy manage the code.
I don't know if this is the best solution but I hope will suit your needs.
models/data.js
// exports empty array
module.exports = [];
controllers/somecontroller.js
var myVar = require('../models/data');
myVar.push({name: 'Alex', age: 20});
console.log(myVar);
// [{ name: 'Alex', age: 20 }]
controllers/anotherController.js
var myVar = require('../models/data');
console.log(myVar);
// This array has value set from somecontroller.js before...
// [{ name: 'Alex', age: 20 }]
// Put new value to array
myVar.push({name: 'John', age: 17});
console.log(myVar);
// Value will be added to an array
// [{ name: 'Alex', age: 20 }, { name: 'John', age: 17}]
There is no way you can share a reference between different files. You shouldn't be.
I have a main.js that then requires different files depending on the triggers that are said
I don't think that's a good idea. All require statements you'll ever need must be at the top of the file.
I also see that You're requiring main.js in total.js and total.js in main.js. The require() function imports the module.exports of the file and assigns it to the namespace you provide. Your code shouldn't be split into files this way. You extract code into separate files only when they're modules by themselves. And if you do, you wouldn't be importing 2 files on each other.
It is also good to note that in javascript, when you assign something to a namespace, It gets copied (cloned) if it's a primitive. If it's an object, both namespaces then refer to the same object
var num = 5;
var prim = num;
prim++; // prim is 6, but num is still 5.
var num = {five:5};
var ob = num;
ob.five = 6;
console.log(num.five) //also 6.
A little hack that works but isn't recommended is using the process variable. You can apply different properties to it and essentially use them like you would the window object in browser-based JS. This little hack will provide a reference to the variable. It can be changed and manipulated and the change will carry over to all files that are required.
But do note that it is not recommended as overriding the process variable could have some unexpected effects and is subject to loss of information should another process interfere.
file1.js:
const s1 = require('./file2');
process.num = 2;
console.log("file1", process.num);
s1.changeNum();
console.log("file1", process.num);
file2.js:
module.exports.changeNum = () => {
process.num = 3;
console.log("file2", process.num);
};
output:
file1 2
file2 3
file1 3
alternatively, to all other answers
getters & setters
var _variableThing = 1223
module.exports = {
get variableThing(){
return _variableThing
},
set variableThing(val){
_variableThing = val
}
}
won't work with direct imports though