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How to avoid DRY by keep re-assigning variable

I have a module where when each function is executed, it reassigns the value of the variable. This variable is stored in the constructor as I want to use it across modules. How can I do this without repeating myself?
function FormatText(data) {
this._data = data;
}
FormatText.prototype.toDowncase = function() {
return this._data = this._data.toLowerCase();
};
FormatText.prototype.deleteWords = function() {
return this._data = this._data.replace(/\W/g, " ");
};
FormatText.prototype.splitWords = function() {
return this._data = this._data.split(/\s+/);
};
FormatText.prototype.filterEntries = function() {
return this._data = this._data.filter(v => !!v);
};
FormatText.prototype.countWords = function() {
return this._data = this._data.reduce((dict, v) => {dict[v] = v in dict ? dict[v] + 1 : 1; return dict}, {});
}
module.exports = FormatText;

JavaScript: Prevent Array.push()

I have a sealed object with an array member on which I want to prevent direct pushes.
var myModule = (function () {
"use strict";
var a = (function () {
var _b = {},
_c = _c = "",
_d = [];
Object.defineProperty(_b, "c", {
get: function () { return _c; }
});
Object.defineProperty(_b, "d", {
get { return _d; }
});
_b.addD = function (newD) {
_d.push(newD);
};
Object.seal(_b);
return _b;
}());
var _something = { B: _b };
return {
Something: _something,
AddD: _b.addD
};
}());
myModule.Something.c = "blah"; // doesn't update = WIN!!
myModule.AddD({}); // pushed = WIN!
myModule.Something.d.push({}); // pushed = sadness
How can I prevent the push?
UPDATE:
Thanks for all the thoughts. I eventually need the JSON to send to the server. It looks like I might need to use an object for the array then figure out a way to generate and return the JSON needed, or change _something to use .slice(). Will play and report.

you could override the push method:
var _d = [];
_d.__proto__.push = function() { return this.length; }
and when you need to use it in your module, call Array.prototype.push:
_b.addD = function (newD) {
Array.prototype.push.call(_d, newD);
};

I haven't done any performance tests on this, but this certainly helps to protect your array.
(function(undefined) {
var protectedArrays = [];
protectArray = function protectArray(arr) {
protectedArrays.push(arr);
return getPrivateUpdater(arr);
}
var isProtected = function(arr) {
return protectedArrays.indexOf(arr)>-1;
}
var getPrivateUpdater = function(arr) {
var ret = {};
Object.keys(funcBackups).forEach(function(funcName) {
ret[funcName] = funcBackups[funcName].bind(arr);
});
return ret;
}
var returnsNewArray = ['Array.prototype.splice'];
var returnsOriginalArray = ['Array.prototype.fill','Array.prototype.reverse','Array.prototype.copyWithin','Array.prototype.sort'];
var returnsLength = ['Array.prototype.push','Array.prototype.unshift'];
var returnsValue = ['Array.prototype.shift','Array.prototype.pop'];
var funcBackups = {};
overwriteFuncs(returnsNewArray, function() { return []; });
overwriteFuncs(returnsOriginalArray, function() { return this; });
overwriteFuncs(returnsLength, function() { return this.length; });
overwriteFuncs(returnsValue, function() { return undefined; });
function overwriteFuncs(funcs, ret) {
for(var i=0,c=funcs.length;i<c;i++)
{
var func = funcs[i];
var funcParts = func.split('.');
var obj = window;
for(var j=0,l=funcParts.length;j<l;j++)
{
(function() {
var part = funcParts[j];
if(j!=l-1) obj = obj[part];
else if(typeof obj[part] === "function")
{
var funcBk = obj[part];
funcBackups[funcBk.name] = funcBk;
obj[part] = renameFunction(funcBk.name, function() {
if(isProtected(this)) return ret.apply(this, arguments);
else return funcBk.apply(this,arguments);
});
}
})();
}
}
}
function renameFunction(name, fn) {
return (new Function("return function (call) { return function " + name +
" () { return call(this, arguments) }; };")())(Function.apply.bind(fn));
};
})();
You would use it like so:
var myArr = [];
var myArrInterface = protectArray(myArr);
myArr.push(5); //Doesn't work, but returns length as expected
myArrInterface.push(5); //Works as normal
This way, you can internally keep a copy of the interface that isn't made global to allow your helper funcs to modify the array as normal, but any attempt to use .push .splice etc will fail, either directly, or using the .bind(myArr,arg) method.
It's still not completely watertight, but a pretty good protector. You could potentially use the Object.defineProperty method to generate protected properties for the first 900 indexes, but I'm not sure of the implications of this. There is also the method Object.preventExtensions() but I'm unaware of a way to undo this effect when you need to change it yourself

Thank you, dandavis!
I used the slice method:
var myModule = (function () {
"use strict";
var a = (function () {
var _b = {},
_c = _c = "",
_d = [];
Object.defineProperty(_b, "c", {
get: function () { return _c; }
});
Object.defineProperty(_b, "d", {
get { return _d.slice(); } // UPDATED
});
_b.updateC = function (newValue) {
_c = newValue;
};
_b.addD = function (newD) {
_d.push(newD);
};
Object.seal(_b);
return _b;
}());
var _something = { B: _b };
return {
Something: _something,
AddD: _b.addD
};
}());
myModule.Something.c = "blah"; // doesn't update = WIN!!
myModule.AddD({}); // pushed = WIN!
myModule.Something.d.push({}); // no more update = happiness
This allows me to protect from direct push calls enforcing some logic.

How to json strinfigy a function instance in javascript?

If I have this code
var node = function(n) {
var name = n;
var children = [];
var finished = false;
var failed = false;
this.getName = function() {
return name
};
this.downloadData = function(obj) {
};
this.getChildren = function() {
return children;
};
this.setChildren = function(c) {
Array.prototype.push.apply(children, c);
};
this.isFinished = function() {
return finished;
};
this.setFinished = function() {
finished = true;
}
this.isFailed = function() {
return failed;
}
this.setFailed = function() {
failed = true;
}
};
How can I convert this into an object like:
var a = new node("a");
var j = JSON.stringify(a);
result
{"name":"a","children":[],"finished":false,"failed":false}
thanks

This could be done by implementing the toJSON function.
If an object being stringified has a property named toJSON whose value
is a function, then the toJSON() method customizes JSON
stringification behavior: instead of the object being serialized, the
value returned by the toJSON() method when called will be serialized.
- Mozilla
eg:
var node = function(n) {
var name = n;
var children = [];
var finished = false;
var failed = false;
this.toJson = function toJson() {
return {"name":name ... };
}
}

You need object properties instead of variables.
So, instead of declaring var name = n;, you would declare this.name = n;. Which would make it look something like
var node = function(n) {
this.name = n;
this.children = [];
this.finished = false;
this.failed = false;
///other functions here
}

Assigning a default value to a javascript using prototyping

I want to be able to assign default values to variables when I'm using prototyping for object creation.
When I try to assign default values to the variables they are always 'undefined'.
I have tried to find the answer but all the possible solutions I have tried dont work.
My questions are:
why do a variable that have I have initiated with a value has the value 'undefined'
how do I solve my problem?
(function() {
EmployeeNS = {};
EmployeeNS.Employee = function() {
var _firstName;
var _lastName;
var _employeeID = 'Unassigned';
}
EmployeeNS.Employee.prototype.setFirstName = function(fName) { this._firstName = fName; };
EmployeeNS.Employee.prototype.getFirstName = function() { return this._firstName; };
EmployeeNS.Employee.prototype.setLastName = function(lName) { this._lastName = lName; };
EmployeeNS.Employee.prototype.getLastName = function() { return this._lastName; };
EmployeeNS.Employee.prototype.setEmployeeID = function(employeeID) { this._employeeID = employeeID; };
EmployeeNS.Employee.prototype.getEmployeeID = function() { return this._employeeID; };
EmployeeNS.Worker = function() {
var _department;
}
EmployeeNS.Worker.prototype = new EmployeeNS.Employee();
EmployeeNS.Worker.prototype.constructor = Worker;
EmployeeNS.Worker.prototype.setDepartment = function(department) { this._department = department; };
EmployeeNS.Worker.prototype.getDepartment = function() { return this._department; };
})();
function createWorker() {
var x = new EmployeeNS.Worker();
x.setFirstName("John");
x.setLastName("Doe");
x.setDepartment("Transport");
var message = x.getFirstName()
+ " "
+ x.getLastName()
+ " (Department: "
+ x.getDepartment()
+ " / EmployeeID: "
+ x.getEmployeeID()
+ ")";
alert(message);
}
Thanks

you can simply make it to work by changing like this,
EmployeeNS.Employee = function() {
this._firstName;
this._lastName;
this._employeeID = 'Unassigned';
}
Try out this way , you can make those variables truly private by wrapping Employee ,
(function() {
EmployeeNS = {};
(function() {
var _firstName;
var _lastName;
var _employeeID = 'Unassigned';
EmployeeNS.Employee = function() {
}
EmployeeNS.Employee.prototype.setFirstName = function(fName) { _firstName = fName; };
EmployeeNS.Employee.prototype.getFirstName = function() { return _firstName; };
EmployeeNS.Employee.prototype.setLastName = function(lName) { _lastName = lName; };
EmployeeNS.Employee.prototype.getLastName = function() { return _lastName; };
EmployeeNS.Employee.prototype.setEmployeeID = function(employeeID) { _employeeID = employeeID; };
EmployeeNS.Employee.prototype.getEmployeeID = function() { return _employeeID; };
})();
(function() {
var _department;
EmployeeNS.Worker = function() {
}
EmployeeNS.Worker.prototype = new EmployeeNS.Employee();
EmployeeNS.Worker.prototype.constructor = Worker;
EmployeeNS.Worker.prototype.setDepartment = function(department) { _department = department; };
EmployeeNS.Worker.prototype.getDepartment = function() { return _department; };
})();
})();
Here is the jsfiddle

If you want instance properties, do it like this:
(function() {
EmployeeNS = {};
EmployeeNS.Employee = function () {
this._firstName = null;
this._lastName = null;
this._employeeID = 'Unassigned';
};
EmployeeNS.Employee.prototype.setFirstName = function(fName) {
this._firstName = fName;
};
})();

JavaScript - how to make it possible to inherit

I'm trying to make it possible to inherit from this class:
function Vehicle(p) {
this.brand = p.brand || "";
this.model = p.model || "";
this.wheels = p.wheels || 0;
}
Vehicle.prototype.getBrand = function () {
return this.brand;
};
Vehicle.prototype.getModel = function () {
return this.model;
};
Vehicle.prototype.getWheels = function () {
return this.wheels;
};
var myVehicle = new Vehicle({
brand: "Mazda",
model: "RX7",
wheels: 4
});
console.log(myVehicle);
I tried doing it this way:
function Vehicle(p) {
this.brand = p.brand || "";
this.model = p.model || "";
this.wheels = p.wheels || 0;
}
Vehicle.prototype.getBrand = function () {
return this.brand;
};
Vehicle.prototype.getModel = function () {
return this.model;
};
Vehicle.prototype.getWheels = function () {
return this.wheels;
};
function Car (){}
Car.prototype = new Vehicle();
Car.prototype.getWheels = function() {
return 4;
};
var myCar = new Car({
brand: "Mazda",
model: "RX7"
});
console.log(myCar);
but it seems like it doesn't work:
> Uncaught TypeError: Cannot read property 'brand' of undefined
Could someone explain to me what's wrong? I guess it's not the write way to implement it but why?

In addition to what #elclanrs said:
function Car () {
Vehicle.apply(this, arguments);
}
var c = function() {};
c.prototype = Vehicle.prototype;
Car.prototype = new c();
Live demo: http://jsfiddle.net/x3K9b/1/

You need to call "super" in Car:
function Car() {
Vehicle.apply(this, arguments);
}
Aside from that you could make p optional by just assigning an empty object for example; that would get rid of the error. And finally point to the right constructor so:
function Vehicle(p) {
p = p || {}; //<=
this.brand = p.brand || "";
this.model = p.model || "";
this.wheels = p.wheels || 0;
}
//...
Car.prototype = new Vehicle();
Car.prototype.constructor = Car; //<=
Edit: Otherwise just use Object.create:
Car.prototype = Object.create(Vehicle.prototype);
That takes care of assigning the constructor and everything.