I have a variable var key = "Something" and want to set a document using this variable as the key.
When I'm trying to do it using settings_ref.update({key: false}); this is obviously using "key" as a string itself.
How can I use a variable as the key of the new data?
You should use the bracket notation:
var obj = {};
obj[key] = false;
settings_ref.update(obj);
See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Property_accessors
Related
I have an object and I want to use object property value as key (simplified):
var App = function() {
this.settings = {
'tetris': {
title: 'Tetris'
},
'galaxian': {
title: 'Galaxian'
}
};
this.gameName = 'tetris';
this.request = {
this.settings[this.gameName].title: 'THIS KEY IS INVALID' // :(
}
};
I know I could assign it as:
this.request[ this.settings[this.gameName].title ] = 'Valid...';
But I wonder if I can define the property name using the object property value?
I am afraid, what you mean is not possible. You can not use a variable as a key in an object literal like this:
var key = "somekey";
var obj = {key: "value"}
The above code will result in an object that has the key key.
You can only use a variable to define an object element like this:
var key = "somekey";
var obj = {};
obj[key] = "value"
Then the object get's an element with the key somekey
EDIT: As stated in the comments, in ECMAScript 6 the support for computed properties in object literals got introduced. However the browser support for the computed properties in object literals is very slim (you can look it up here under syntax -> object literals). For example IE 11 has no support for it, neither has Chrome 43.
Computed property names will be introduced in ECMAScript edition 6, they're in the current draft, so you can do:
this.request = {
[this.settings[this.gameName].title]
}
They're reasonably well supported now, see MDN for more detail.
You can't define literal objects with computed property names; you have to assign them.
In other words, you can either define a literal object using {...} notation if the property name is well-known, or assign values into keys in a map using x[prop] = v notation if the property name is computed.
Think of your JS objects as being either objects or maps, but not both. If the JS object has well-known property names then it's acting as an object:
var obj = {
wellKnownPropertyName = 'value';
};
var value = obj.wellKnownPropertyName;
But if the property name is computed then it's not really a property of an object but more like a key in a map, and should be assigned (and read) as such:
var map = {};
var key = getUnknownKeyFromSomewhere();
map[key] = 'value';
var value = map[key];
I am building some UI page using jQuery. In some function, i am creating a JavaScript object as
var key = "04:52:00";
var val = 13.21;
var data = {
key : val
};
When I try to loop through the data object like,
for(var category in data) {
alert(category);
var points = data[category];
alert(points);
}
In the above, I am getting the value of val variable correctly as 13.21, but I am not getting key variable value, instead in the alert(category);, I am getting key not 04:52:00.
I am not much familiar with jQuery/JavaScript.
You have to use bracket notation to use variables as keys, when using dot notation or when creating an object, the key doesn't have to be quoted, and the literal string will be used as a key instead of the variable.
var key = "04:52:00";
var val = 13.21;
var data = {};
data[key] = val;
When initializing an object using a literal, like you're doing, you can't use variables for keys.
You'll have to use the bracket notation instead:
var data = {};
data[key] = val;
I have a Javascipt object which I use as dictionary
var obj={
xxx:'1'
yyy:'2'
}
However -
xxx and yyy should be a jQuery object.
something like :
var obj =
{
$('#div1'):'1' ,
$('#div2'):'2'
}
is it possible ?
also, How can I get the "value" for key $('#div2') ?
p.s.
I the $.data cant help me here since its also a key value
and i need in the key - object Type also.
Object keys can only be strings ( or Symbol), period. See Member Operators - Property Names # MDN.
Choose a reasonable string representation, and use that. In this case, I'd say the selector string looks like a decent choice:
{
'#div1': '1',
'#div2': '2'
}
also, How can I get the "value" for key $('#div2') ?
Use one of the member operators, either dot notation
var obj = { /* stuff */ };
var value = obj.propertyName;
console.log(value);
or bracket notation (more useful for property names not known until runtime):
var value = obj['propertyName'];
Use a WeakMap which works like a dictionary where the key can be anything. Note that you cannot list all the keys of the map
const aMap = new WeakMap;
const anObject = {};
aMap.set(Number, "It's the Number class")
aMap.set(anObject, "It's an object")
console.log(aMap.get(Number)) // It's the Number class
console.log(aMap.get(anObject)) // It's an object
I'm trying to create an array that maps strings to variables. It seems that the array stores the current value of the variable instead of storing a reference to the variable.
var name = "foo";
var array = [];
array["reference"] = name;
name = "bar";
// Still returns "foo" when I'd like it to return "bar."
array["reference"];
Is there a way to make the array refer to the variable?
Put an object into the array instead:
var name = {};
name.title = "foo";
var array = [];
array["reference"] = name;
name.title = "bar";
// now returns "bar"
array["reference"].title;
You can't.
JavaScript always pass by value. And everything is an object; var stores the pointer, hence it's pass by pointer's value.
If your name = "bar" is supposed to be inside a function, you'll need to pass in the whole array instead. The function will then need to change it using array["reference"] = "bar".
Btw, [] is an array literal. {} is an object literal.
That array["reference"] works because an Array is also an object, but array is meant to be accessed by 0-based index. You probably want to use {} instead.
And foo["bar"] is equivalent to foo.bar. The longer syntax is more useful if the key can be dynamic, e.g., foo[bar], not at all the same with foo.bar (or if you want to use a minimizer like Google's Closure Compiler).
Try pushing an object to the array instead and altering values within it.
var ar = [];
var obj = {value: 10};
ar[ar.length] = obj;
obj.value = 12;
alert(ar[0].value);
My solution to saving a reference is to pass a function instead:
If the variable you want to reference is called myTarget, then use:
myRef = function (newVal) {
if (newVal != undefined) myTarget = newVal;
return myTarget;
}
To read the value, use myRef();. To set the value, use myRef(<the value you want to set>);.
Helpfully, you can also assign this to an array element as well:
var myArray = [myRef];
Then use myArray[0]() to read and myArray[0](<new value>) to write.
Disclaimer: I've only tested this with a numerical target as that is my use case.
My solution to saving a reference is to pass a function instead:
If the variable you want to reference is called 'myTarget', then use:
myRef = function (newVal) {
if (newVal != undefined)
myTarget = newVal;
return myTarget;
}
To read the value, use myRef();. To set the value, use myRef(value_to_set);.
Helpfully, you can also assign this to an array element as well:
var myArray = [myRef];
Then use myArray0 to read and myArray[0](value_to_set) to write.
Disclaimer: I've only tested this with a numerical target as that is my use case.
I defined a variable which will get user's input:
var input = USER_INPUT;
then, I create an object which will use this input as an variable name inside the object:
var obj = { input: Car.newCar(...)}
Then, I try to access the obj[input], but it returns to me undefined. Is it so that in javascript, I can not use variable as an object's variable name?
If I would like to define a object which has vary variable name and variable value, how can I do?
So I guess you want the store the input under a key named after the input itself.
You can assign the value returned by Car.newCar() by using the [] method:
var input = "some text";
var obj = {};
obj[input] = Car.newCar();
Sorry changed my answer after re-reading the question
var USER_INPUT = 'something';
var obj = {};
obj[USER_INPUT] = 'value';
obj.something ; //# => value
obj['something'] ; //# => value
obj[USER_INPUT]; //# => value