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How to access props inside a filter with an argument in React [duplicate]

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Add a property to a JavaScript object using a variable as the name? [duplicate]
(14 answers)
Closed 7 years ago.
I want to add a new property to 'myObj', name it 'string1' and give it a value of 'string2', but when I do it it returns 'undefined:
var myObj = new Object;
var a = 'string1';
var b = 'string2';
myObj.a = b;
alert(myObj.string1); //Returns 'undefined'
alert(myObj.a); //Returns 'string2'
In other words: How do I create an object property and give it the name stored in the variable, but not the name of the variable itself?

There's the dot notation and the bracket notation
myObj[a] = b;

ES6 introduces computed property names, which allow you to do
var myObj = {[a]: b};

Dot notation and the properties are equivalent. So you would accomplish like so:
// const myObj = new Object();
const myObj = {};
const a = 'string1';
myObj[a] = 'whatever';
alert(myObj.string1);
(alerts "whatever")

Ecu, if you do myObj.a, then it looks for the property named a of myObj.
If you do myObj[a] =b then it looks for the a.valueOf() property of myObj.

Oneliner:
obj = (function(attr, val){ var a = {}; a[attr]=val; return a; })('hash', 5);
Or:
attr = 'hash';
val = 5;
var obj = (obj={}, obj[attr]=val, obj);
Anything shorter?

You could just use this:
function createObject(propName, propValue){
this[propName] = propValue;
}
var myObj1 = new createObject('string1','string2');
Anything you pass as the first parameter will be the property name, and the second parameter is the property value.

You cannot use a variable to access a property via dot notation, instead use the array notation.
var obj= {
'name' : 'jroi'
};
var a = 'name';
alert(obj.a); //will not work
alert(obj[a]); //should work and alert jroi'

As $scope is an object, you can try with JavaScript by:
$scope['something'] = 'hey'
It is equal to:
$scope.something = 'hey'
I created a fiddle to test.

The following demonstrates an alternative approach for returning a key pair object using the form of (a, b). The first example uses the string 'key' as the property name, and 'val' as the value.
Example #1:
(function(o,a,b){return o[a]=b,o})({},'key','val');
Example: #2:
var obj = { foo: 'bar' };
(function(o,a,b){return o[a]=b,o})(obj,'key','val');
As shown in the second example, this can modify existing objects, too (if property is already defined in the object, value will be overwritten).
Result #1: { key: 'val' }
Result #2: { foo: 'bar', key: 'val' }

Why does error occur at var obj={'A':'B','C':obj['A']};?

I want to create an javascript object, which value of "C" copies value of "A" :
var obj={
'A':'some complex function returns a string',
'C':obj['A']
};
But it has errors. I try to check if key 'A' really created:
var f=function(str){
console.log(str);
return str;
};
var obj={
[f('A')]:[f('B')],
"C":obj['A']
};
which prints
B
A
and then errors. Which means 'A' created but it still says obj['A'] is not defined. Why would that happen?

Your current attempt obviously fails because by the time the code constructs new object the value of obj variable was not assigned yet.
You could check it by using
var obj = { C: typeof obj}
I want to create an javascript object, which value of "C" copies value of "A"
If you want C to always reflect the value of A you could use
var obj = {
A: 'Some value',
get C() {
return this.A;
}
}
Or split obj declaration
var obj = { A: 'Some Value' };
obj.C = obj.A

You get the error because obj was not yet defined when you attempted to acces it from inside of it.
To make your code work you could use a getter.
The get syntax binds an object property to a function that will be
called when that property is looked up. - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/get
Also you do not need quotes for your object properties.
Quotes can be omitted if the property name is a numeric literal
or a valid identifier name.
var obj = {
A : 'Hello',
get C() {
return this.A;
}
};
console.log(obj.C);

You can not reference a variable that has not created yet. You can do it like this.
var obj = { 'A' : 'some complex function returns a string' }
obj['C'] = obj['A']

Mongoose update on a string variable not working? [duplicate]

It's difficult to explain the case by words, let me give an example:
var myObj = {
'name': 'Umut',
'age' : 34
};
var prop = 'name';
var value = 'Onur';
myObj[name] = value; // This does not work
eval('myObj.' + name) = value; //Bad coding ;)
How can I set a variable property with variable value in a JavaScript object?

myObj[prop] = value;
That should work. You mixed up the name of the variable and its value. But indexing an object with strings to get at its properties works fine in JavaScript.

myObj.name=value
or
myObj['name']=value (Quotes are required)
Both of these are interchangeable.
Edit: I'm guessing you meant myObj[prop] = value, instead of myObj[name] = value. Second syntax works fine: http://jsfiddle.net/waitinforatrain/dNjvb/1/

You can get the property the same way as you set it.
foo = {
bar: "value"
}
You set the value
foo["bar"] = "baz";
To get the value
foo["bar"]
will return "baz".

You could also create something that would be similar to a value object (vo);
SomeModelClassNameVO.js;
function SomeModelClassNameVO(name,id) {
this.name = name;
this.id = id;
}
Than you can just do;
var someModelClassNameVO = new someModelClassNameVO('name',1);
console.log(someModelClassNameVO.name);

simple as this
myObj.name = value;

When you create an object myObj as you have, think of it more like a dictionary. In this case, it has two keys, name, and age.
You can access these dictionaries in two ways:
Like an array (e.g. myObj[name]); or
Like a property (e.g. myObj.name); do note that some properties are reserved, so the first method is preferred.
You should be able to access it as a property without any problems. However, to access it as an array, you'll need to treat the key like a string.
myObj["name"]
Otherwise, javascript will assume that name is a variable, and since you haven't created a variable called name, it won't be able to access the key you're expecting.

You could do the following:
var currentObj = {
name: 'Umut',
age : 34
};
var newValues = {
name: 'Onur',
}
Option 1:
currentObj = Object.assign(currentObj, newValues);
Option 2:
currentObj = {...currentObj, ...newValues};
Option 3:
Object.keys(newValues).forEach(key => {
currentObj[key] = newValues[key];
});

Get #-identifier of Object in JavaScript

I have an JavaScript object looking like this:
Object {#attributes: Object,…}
So how can I access the #attributes-Object?

parent["#attributes"], thus:
var parent = { "#attributes" : someObj} ;
console.log(parent["#attributes"]);
In JS, all property names can be used as named array elements. Most (i.e. those without spaces etc) can be used as bare property names.
var foo = { bar: 1};
foo.bar = 2 // or
foo["bar"] = 2

You can use the bracket notation:
var myObject = { '#attributes': 'foo' };
var result = myObject['#attributes']; // foo

Javascript setter and getter with key for object

I have an object in a variable var o={};
I want to do something like what .push() method doing in array for my object.
JS code:
// Array:
var ar=[];
ar.push('omid');
ar.push('F');
var got=ar[1];
// above code is standard but not what I'm looking for !
/*-------------------------------------*/
// Object:
var obj={};
/* obj.push('key','value'); // I want do something like this
var got2=obj.getVal('key'); // And this
*/
Is this possible at all ?

var obj = {}
// use this if you are hardcoding the key names
obj.key = 'value'
obj.key // => 'value'
// use this if you have strings with the key names in them
obj['key2'] = 'value'
obj['key2'] // => 'value'
// also use the second method if you have keys with odd names
obj.! = 'value' // => SyntaxError
obj['!'] = 'value' // => OK

Since Object-Literals use a Key->Value model, there is no JS method to "push" a value.
You can either use Dot Notation:
var Obj = {};
Obj.foo = "bar";
console.log(Obj);
Or Bracket Notation:
var Obj = {},
foo = "foo";
Obj[foo] = "bar";
Obj["bar"] = "foo";
console.log(Obj);
Consider reading https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Working_with_Objects, as arming yourself with this knowledge will be invaluable in the future.

Here is some javascript magic that makes it work.
Take a look.
var obj = {};
Object.defineProperty(obj,'push',{
value:function(x,y){
this[x]=y;
}
});
obj.push('name','whattttt'); <<<this works!!!
obj;
//{name:'whattttt'}
obj.name or obj['name']..
//whattttt
The reason i defined .push function using Object.defineProperty because i didn't want it to show up as a property of object. So if you have 3 items in object this would have always been the 4th one. And mess up the loops always. However, using this method. You can make properties hidden but accessible.
Though i don't know why you would use this method when there is already a easy way to do it.
to assign a value do this
obj.variable = 'value';
if value key is number or weird do this...
obj[1] = 'yes';
to access number or weird name you also do that
obj[1];
and finally to assign random keys or key that has been generated in code, not hard coded, than use this form too.
var person= 'him';
obj[him]='hello';