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.map() unable to access Object's this.function

Thanks in advance for any responses:
I don't think this is a duplicate: I reviewed that article in the first comment, that is just a general breakdown of objects and using "this" within javascript.
My other this.function's perform just fine, so I at least have the basics of JS Obj's figured out.
This issue is related to using .map() with a this.function within a constructed object.
The following Google Appscript code uses .map() to update a string in a 2d array. [[string, int],[string, int]]
For some reason, when using .map() it is am unable to access the function "this.removeLeadingZero". If that same function is placed outside of the OBJ it can be called and everything works just fine. For some reason the system claims row[0] is an [object, Object] but when I typeof(row[0]) it returns "string" as it should.
Error: TypeError: Cannot find function removeLeadingZero in object [object Object]. (line 106, file "DEEP UPC MATCH")
Is there any issue using this.function's with .map() inside an object or am I using an incorrect syntax?
function test2DMapping(){
var tool = new WorkingMappingExample()
var boot = tool.arrayBuild();
Logger.log(boot)
}
function WorkingMappingExample(){
this.arr= [["01234", 100],["401234", 101],["012340", 13],["01234", 0422141],["01234", 2],["12340",3],["01234", 1],["01234", 2],["12340",3],["01234", 1],["01234", 2],["12340",3],["01234", 1],["01234", 2],["12340",3]];
//mapping appears faster that normal iterations
this.arrayBuild = function(){
var newArray1 =
this.arr.map( function( row ) {
**var mUPC = removeLeadingZero2(row[0])** //working
**var mUPC = this.removeLeadingZero(row[0])** // not working
var index = row[1]
Logger.log(mUPC + " " + index)
row = [mUPC, index]
return row
} )
return newArray1;
};
}; //end of OBJ
//THE NEXT 2 FUNCTIONS ARE WORKING OUTSIDE OF THE OBJECT
function removeLeadingZero2(upc){
try {
if (typeof(upc[0]) == "string"){
return upc.replace(/^0+/, '')
} else {
var stringer = upc.toString();
return stringer.replace(/^0+/, '')
}
} catch (err) {
Logger.log(err);
return upc;
}
}
function trimFirstTwoLastOne (upc) {
try {
return upc.substring(2, upc.length - 1); //takes off the first 2 #'s off and the last 1 #'s
} catch (err) {
Logger.log(err);
return upc;
}
}

Inside the function that you pass to map, this doesn't refer to what you think it does. The mapping function has its own this, which refers to window, normally:
var newArray1 = this.arr.map(function(row) {
// this === window
var mUPC = this.removeLeadingZero(row[0]);
var index = row[1];
Logger.log(mUPC + " " + index);
return [mUPC, index];
});
You have four options:
Array#map takes a thisArg which you can use to tell map what the this object in the function should be:
var newArray1 = this.arr.map(function(row) {
// this === (outer this)
var mUPC = this.removeLeadingZero(row[0]);
// ...
}, this); // pass a thisArg
Manually bind the function:
var newArray1 = this.arr.map(function(row) {
// this === (outer this)
var mUPC = this.removeLeadingZero(row[0]);
// ...
}.bind(this)); // bind the function to this
Store a reference to the outer this:
var self = this;
var newArray1 = this.arr.map(function(row) {
// self === (outer this)
var mUPC = self.removeLeadingZero(row[0]);
// ...
});
Use an arrow function:
var newArray1 = this.arr.map(row => {
// this === (outer this)
var mUPC = this.removeLeadingZero(row[0]);
// ...
});
Additionally, you could stop using this and new.

I have solved this issue and below is the answer in case anyone else runs into this:
this needs to be placed into a variable:
var _this = this;
and then you can call it within the object:
var mUPC = _this.removeLeadingZero(row[0])
Javascript scope strikes again!

How do you populate a dynamic variable in AngularJS

The following code gives me the error "Cannot read property PERSON1 of null". If I comment out the line where I try to assign the dynamic variable and uncomment the alert line it pops up alerts with each successive person's name.
function fillInternalRepData() {
var internalRepList = null;
console.log("Querying Table for internal reps");
queryTable(//..blabla..//, "false", function (callbackResp) {
internalRepList = callbackResp;
// alert("TRIGGERED"); //WORKS
// alert(internalRepList.length); //WORKS
angular.forEach(internalRepList, function (rep) {
repName = rep.such;
$scope.internalReps[repName].such = repName;
//alert(repName); //WORKS WHEN LINE ABOVE IS COMMENTED OUT
});
}); //get list of internal reps
I simply want to create/add to the $scope.internalReps object so that I can add stuff to it like $scope.internalReps.PERSON1.Name = "Whatever"; $scope.internalReps.PERSON1.Salary = 100000;

Try adding an empty object for the "internalReps" before your forEach loop. It doesn't look like you've declared the object yet, so it can't dynamically add to a null object.
$scope.internalReps = {};
angular.forEach(internalRepList, function (rep) {
repName = rep.such;
$scope.internalReps[repName] = {};
$scope.internalReps[repName].such = repName;
//alert(repName);
});

var internalReps = {};
angular.forEach(internalRepList, function (rep) {
repName = rep.such;
internalReps[repName] = { such: "" };
internalReps[repName].such = repName;
//alert(internalReps[repName].such);
});
That worked. Thanks for the help!

Phaser - For loop throwing "TypeError: Cannot read property 'length' of undefined"

I am trying to build a simple game using Phaser.js and I've come across an issue when looping through an array.
var EnemyGroup = function(enemies) {
game.add.group();
this.enemies = enemies;
this.addEnemies(this.enemies);
//return this;
};
EnemyGroup.prototype = Object.create(Phaser.Group.prototype);
EnemyGroup.prototype.constructor = EnemyGroup;
EnemyGroup.prototype.addEnemies = function(enemies) {
console.log(enemies.length);
for (var i=0;i<enemies.length;i++) {
console.log(i);
this.add(enemies[i]);
}
console.log('done');
};
Above, when I create an instance of an EnemyGroup, I call the function this.addEnemies. Which, after it loops through the array, throws the error:
TypeError: Cannot read property 'length' of undefined
To understand why, I had the console log the count of the array and log the index it is currently on as it loops. There is only 1 object in the array.
The output is:
1 <-the array count (correct)
0 <-the index it is on (also correct as there is only one object in the array)
TypeError: Cannot read property 'length' of undefined <-the error
I check to see if the error is being caused outside of the for loop by having the console log Done... but it does not log this, so I know it's messing up somewhere in the for loop.

Simple: you forgot to add this when referencing enemies on addEnemies()
var EnemyGroup = function(enemies) {
game.add.group();
this.enemies = enemies;
this.addEnemies(this.enemies);
//return this;
};
EnemyGroup.prototype = Object.create(Phaser.Group.prototype);
EnemyGroup.prototype.constructor = EnemyGroup;
EnemyGroup.prototype.addEnemies = function(enemies) {
console.log(this.enemies.length);
for (var i=0;i<this.enemies.length;i++) {
console.log(i);
this.add(this.enemies[i]);
}
console.log('done');
};
Related problem: Why is there no implicit this in JavaScript

var EnemyGroup = function(game) {
Phaser.Group.call(this, game);
};
EnemyGroup.prototype = Object.create(Phaser.Group.prototype);
EnemyGroup.prototype.constructor = EnemyGroup;
EnemyGroup.prototype.addEnemies = function(enemies) {
for (var i=0;i<enemies.length;i++) {
if (enemies[i]) {
this.add(enemies[i]);
}
}
};
Then in main.js:
enemyGroup = new EnemyGroup(game);
enemyGroup.addEnemies(pikas);

Javascript custom eventlistener not working?

These are the sections of code from my custom event listeners that is not working.
Why does this return '-1' var idx=functionList[eventType].indexOf(callback) when they are the same?
When I use the following in the myObject.removeCustomEventListenr() method
console.log(functionList[eventType][0]) /*the console shows
function(){console.log('firedEvent')*/
console.log(callback) /*the console shows
function(){console.log('firedEvent')*/
both the same thing so why does it not work
Below is the full part that is causing trouble
var myObject = {}
var functionList = {}
myObject.addCustomEventListener = function(eventType,callback){
if(!functionList[eventType]){
functionList[eventType] = []
}
functionList[eventType].push(callback)
//creates functionList.start[0] = function(){console.log('firedEvent')}
}
myObject.removeCustomEventListener = function(eventType,callback){
if(functionList[eventType]){
var idx = functionList[eventType].indexOf(callback)
console.log(idx) //logs '-1' should however match and return 0
if(idx!=-1){
functionList[eventType].splice(idx,1)
console.log('removed')//obviously does not remove the function form the array
}
}
}
myObject.addCustomEventListener('start',function(){console.log('firedEvent')})
myObject.removeCustomEventListener('start',function(){console.log('firedEvent')})
Please explain why this occurs and how I can fix it?
Thanks

The problem is that you're passing references to 2 different functions to the add and remove functions, here:
myObject.addCustomEventListener('start',function(){console.log('firedEvent')})
myObject.removeCustomEventListener('start',function(){console.log('firedEvent')})
While the code in the functions is the same, they're both separate objects as far as JavaScript is concerned, meaning you can't find one when passing the other to indexOf()
This should work:
var callback = function(){
console.log('firedEvent')
};
myObject.addCustomEventListener('start', callback)
myObject.removeCustomEventListener('start', callback)
var myObject = {}
var functionList = {}
myObject.addCustomEventListener = function(eventType,callback){
if(!functionList[eventType]){
functionList[eventType] = []
}
functionList[eventType].push(callback)
//creates functionList.start[0] = function(){console.log('firedEvent')}
}
myObject.removeCustomEventListener = function(eventType,callback){
if(functionList[eventType]){
var idx = functionList[eventType].indexOf(callback)
console.log(idx) //logs '-1' should however match and return 0
if(idx!=-1){
functionList[eventType].splice(idx,1)
alert('removed')//obviously does not remove the function form the array
}
}
}
var callback = function(){
console.log('firedEvent')
};
myObject.addCustomEventListener('start', callback);
myObject.removeCustomEventListener('start', callback);

unable to change javascript object property with async, nodejs and mongodb

I have the following code:
exports.home = function(Comment,User,Activity){
return function(req, res){
var get_url = req.url.split(/\?/)[1];
if (!req.user)
{
res.writeHead(302, {
'Location': '/'
});
res.end();
return;
}
var posts_id_array = req.user.posts_id_array;
var stocks_array = req.user.watch_list;
var subscribe_to_arr = req.user.subscribe_to;
User.find({_id:{$ne:req.user._id, $nin:subscribe_to_arr}}).sort('-_id').limit(10).exec(function(err_user, users){
Activity.find({$or:[{owner_id : {$in :subscribe_to_arr}},{owner_id:req.user._id}]}).sort('-time_stamp').limit(20).exec(function(err_post,activities){
if( err_post || !activities) {
res.render('home',{user:req.user,stocks:JSON.stringify(stocks_array)});
}
else
{
var funcArr = [];
var hasPost = ["publish","comment","like"];
var notPost = ["add_stock","delete_stock"];
for(var i =0;i<activities.length;i++)
{
if(hasPost.indexOf(activities[i].type)!=-1){
var fobj = {
act: activities[i],
f:function(callback){
var test = this.act;
var comments = test.post.comments;
Comment.find({_id:{$in:comments}},function(err,_comments){
console.log("test.post.comments");
//console.log(test.post.comments);
console.log("comments ");
console.log(_comments);
console.log("type");
console.log(typeof test);
console.log("cloning obj");
// obj = JSON.parse(JSON.stringify(test)); // cloning obj
console.log(test);
console.log("setting value of comments");
**console.log(test.post.comments = _comments);** //unable to change test.post.comments
console.log("after assignment");
console.log(test.post.comments); // remain unchanged but work with obj.post.comments if I clone test as obj and use obj instead.
callback(null,test);
});
}
}
funcArr.push(fobj.f.bind(fobj));
}else{
var fobj = {
act: activities[i],
f :function(callback){
callback(null,this.act);
}
}
funcArr.push(fobj.f.bind(fobj));
}
}
async.series(funcArr,function(err,resArr){
console.log("resArr");
console.log(resArr);
res.render('home',{user:req.user,posts:JSON.stringify(resArr),stocks:JSON.stringify(stocks_array), other_users:JSON.stringify(users)});
});
}
});
}) // end of User.find
}// end of return function(req,res);
}
I want to update the post.comments property of the "test" object (see ** parts), but I was unable to do so. However, when I cloned the "test" object as "obj" then set "obj.post.comments" it works. Why is it the case? Is it because I messed up some scoping issues?
Thanks.

I have solved this problem myself. It turns out that I have store mongodb's Schema.Types.ObjectId in the test.post.comments which after some messing around I found cannot be overwritten. When I create a clone of the test object as "obj", the Schema.Types.ObjectId object in obj.post.comments is stored at a different location which allows for modification. My conjecture is that test.post.comments points to a Schema.Types.ObjectId within mongodb itself and therefore cannot be overwritten. When I create a copy of the test object, the problem is therefore resolved.

var test = this.act.concat();
use this instead.
because arrays substitution in js actually does not copy array but refer original adresses.
for example
var test = ['A','B','C','D'];
var copied = test;
test[0] = 0;
copied[1] = 0;
console.log(test) //0,0,'C','D'
console.log(copied) //0,0,'C','D'
so to avoid this issue, You can use .concat() to copy array
if you do not add anything, it will be used as copying.
var test = ['A','B','C','D'];
var copied = test.concat();
test[0] = 0;
copied[1] = 0;
console.log(test) //0,'B','C','D'
console.log(copied) //'A',0,'C','D'