How do I access 'a' below?
var test = function () {
return {
'a' : 1,
'b' : this.a + 1 //doesn't work
};
};
You can't do it this way. When you are in the process of constructing an object (that's what you actually do using the curly braces), there is no way to access it's properties before it is constructed.
var test = function () {
var o = {};
o['a'] = 1;
o['b'] = o['a'] + 1;
return o;
};
var t = function ()
{
return new x();
};
var x = function ()
{
this.a = 1;
this.b = this.a + 1; //works
}
abstract a layer
edited for formatting, and noting that this is shifting from OLN
You can't Object Literal Notion does not support this access
var test = function () {
//private members
var a = 1;
var b = a + 1;
//public interface
return {
geta : function () {
return a;
},
getb : function () {
return b;
}
}
}();
Related
So i have this code:
function Class1() {
this.i = 1;
var that=this;
function nn() {
return 21;
}
this.aa = function() {
nn();
};
this.bb = function() {
this.aa();
};
this.cc = function() {
this.bb();
};
}
var o = new Class1();
var b=o.cc();
alert(b); //undefined
But when the alert is fired, I get an undefined error and not 21, Does the private method can not use a return? Thanks!
When using the function() {} syntax to define a function, you always explicitly need to return the value, i.e. not only from nn, but from all intermediate functions as well.
function Class1() {
this.i = 1;
var that = this;
function nn() {
return 21;
}
this.aa = function() {
return nn();
}
this.bb = function() {
return this.aa();
}
this.cc = function() {
return this.bb();
}
}
var o = new Class1();
var b = o.cc();
alert(b); // "21"
Apart from the answer above, the 'this' context seems weird in your functions. Maybe you are better of with arrow functions if you dont want to bind the this context to each function. I also think that it is better to actually separate private and public functions when using a 'class' like this.
function Class1() {
var _nn = function () {
return 21;
}
var _aa = function () {
return _nn();
}
var _bb = function () {
return _aa();
}
var cc = function () {
return _bb();
};
return {
cc
};
}
var o = new Class1();
var a = o.cc();
console.log(a);
Much easier to understand that it is only cc that is a public function.
So with arrow function it would instead look like this, and you can use the Class1 this context inside of your private functions without doing
var that = this; or using bind.
function Class1() {
this.privateThing = 'private';
var _nn = () => { return this.privateThing; };
var _aa = () => { return _nn(); };
var _bb = () => { return _aa(); };
var cc = () => { return _bb(); };
return {
cc
};
}
I want add new function after i have created objects . I try write some code but it not right.
//
Sorry my description don't clear. I want after i create an object i can add function for this object to do something. Hope someone can understand my english :(
http://fiddle.jshell.net/7LnLerdt/
function Add(a,b){
var _self = this;
var a = a;
var b = b;
}
Add.prototype.doAdd = function(){
var rs = this.a+this.b;
if(rs < 10){
this.lessThanTen();
}else{
this.moreThanTen();
}
};
Add.prototype.moreThanTen = function(callback) {
if(callback){
callback.call(this);
}
};
Add.prototype.lessThanTen = function(callback) {
if(callback){
callback.call(this);
}
};
var add = new Add();
add.moreThanTen(function(){
console.log("moreThanTen");
});
add.lessThanTen(function(){
console.log("lessThanTen")
});
add.doAdd();
The code where you are "assigning" callbacks is not how it works. It just executes the method, it does not magically just assign the callback. The callbacks would need to be passed into the doAdd method or you need to assign the callbacks in a different manner.
If you want to add properties to object use this code instead:
function Add(a,b){
this.a = a;
this.b = b;
}
If you want to add callbacks use this:
Add.prototype.addCallbacks(less, more) {
this.less = less;
this.more = more;
};
Add.prototype.moreThanTen = function(callback) {
if(this.more){
this.more.call(this);
}
};
Add.prototype.lessThanTen = function(callback) {
if(this.less){
this.less.call(this);
}
};
and then
var add = new Add();
add.addCallbacks(function(){
console.log("lessThanTen")
}, function(){
console.log("moreThanTen");
});
You have a couple of problems. First, using var will declare a local variable, so it will not be accessible outside that function. If you want to create a member variable, use this. instead (as jcubic pointed out).
function Add(a, b) {
this.a = a;
this.b = b;
}
Second, you are not adding the callbacks correctly. Your code is executing the callback immediately, but (I think) what you really want to do is save the callback and execute it later.
function Add(a, b) {
this.a = a;
this.b = b;
this.moreThanTenCallbacks = [];
this.lessThanTenCallbacks = [];
}
Add.prototype.moreThanTen = function(callback) {
moreThanTenCallbacks.push(callback);
};
Add.prototype.lessThanTen = function(callback) {
lessThanTenCallbacks.push(callback);
};
Add.prototype.executeCallback = function(callbacks) {
for (var i = 0; i < callbacks.length; ++i) {
if (callback) {
callback();
}
}
};
Add.prototype.doAdd = function() {
var rs = this.a + this.b;
if (rs < 10) {
this.executeCallback(this.lessThanTenCallbacks);
} else {
// NOTE: this will execute moreThanTen callbacks even if the result equals 10!
// Are you sure that is what you want?
this.executeCallback(this.moreThanTenCallbacks);
}
};
I need a way to rewrite a javascript variable which I have written.
Here is what I have:
var TEST = new function() {
var a = 'a';
var b = 'b';
this.c = 'c';
this.getC = function() {
return this.c;
}
};
I am not very comfortable with the new keyword in front of the function(which even jslint/jshint do not like much).
I do not want key:value pair notation, which can be achieved with this code:
var TEST = function() {
return {
a : 'a',
b : 'b',
c : 'c',
getC : function() {
return this.c;
}
}
}();
Please suggest any better way, other than the key:value pair notations.
Fiddle link depicting the above problem.
http://jsfiddle.net/dizel3d/u1w6m9tb/3/ JSHint valid.
var TEST = (function() {
function Test() {
var a = 'a';
var b = 'b';
this.c = 'c';
this.getC = function() {
return this.c;
};
}
return new Test();
})();
Make it into a class:
function Thing(){
this.a="a";
this.b="b";
this.c="c";
}
Thing.prototype.getC=function(){return this.c;}
(new Thing()).getC(); //"c"
i think i did not understand javascript module pattern.
I just create this module:
var mycompany = {};
mycompany.mymodule = (function() {
var my = {};
var count = 0;
my.init = function(value) {
_setCount(value);
}
// private functions
var _setCount = function(newValue) {
count = newValue;
}
var _getCount = function() {
return count;
}
my.incrementCount = function() {
_setCount(_getCount() + 1);
}
my.degreeseCount = function() {
_setCount(_getCount() - 1);
}
my.status = function() {
return count;
}
return my;
})();
var a = mycompany.mymodule;
var b = mycompany.mymodule;
console.debug(a, 'A at beginning');
console.debug(a, 'B at beginning');
a.init(5);
b.init(2);
console.log('A: ' + a.status()); // return 2 (wtf!)
console.log('B: ' + b.status()); // return 2`
Where is the mistake?
I thought that my code would have returned to me not 2 value, but 5.
What's the reason?
a and b are the exact same objects.
var a = mycompany.mymodule;
var b = mycompany.mymodule;
What you want to do is create two different objects which have the same prototype. Something similar to this:
mycompany.mymodule = (function () {
var my = function () {};
my.prototype.init = function (value) {
_setCount(value);
};
my.prototype.incrementCount = ...
// ...
return my;
}());
a = new mycompany.mymodule();
b = new mycompany.mymodule();
a.init(5);
b.init(2);
For more info, research "javascript prototypal inheritance"
In JavaScript, objects are passed by reference, not copied.
To explain further, here is a simplified version of your code:
var pkg = (function () {
var x = {};
return x;
}());
var a = pkg;
var b = pkg;
You do not create two separate objects but only reference the object pointed at by pkg from both a and b. a and b are exactly the same.
a === b // true
This means that calling a method on a you are ultimately doing the same to b (it points to the same object—x.)
You don't want to use the module pattern for this. You want the usual constructor+prototype.
function Pkg() {
this.count = 0;
};
Pkg.prototype.init = function (count) { this.count = count; };
var a = new Pkg();
var b = new Pkg();
a === b // false
a.init(2);
a.count === 2 // true
b.count === 2 // false
Here is a good read about module pattern.
Ok, so I know through closure I can do something like this:
var x,
obj = {
init: function() {
x = 123;
},
func: function() {
return x;
}
};
obj.init();
obj.func();
==> 123
However, I would like to externally be able to apply values for x (outside of the object, and later on)... I thought that perhaps I could just do:
var obj = {
init: function() {
// do something nice here...
},
func: function() {
return x;
}
};
var foo = {
doIt: function() {
var init = obj.init;
var x;
obj.init = function() {
x = 456;
init.apply(obj);
}
obj.init();
obj.func();
}
};
foo.doIt();
==> (error) x is not defined
However, it doesn't work.. Is this possible to do somehow?
Thanks.
You could create objects of your type using the new operator, and set the property on that object.
function Foo() {
this.init = function() {
this.x = -1;
};
this.func = function() {
return this.x;
};
}
var o = new Foo;
o.x = 941;
o.func(); // 941
o.x = 22;
o.func(); // 22