This question already has answers here:
How can I access object properties containing special characters?
(2 answers)
Closed 7 years ago.
I'm building an Elasticsearch search interface. My method is to build the initial query object, and then alter it depending on the user input.
In the filter part of my object, I have
'filter':{
'and':[
{
'term' : {
'terms.region.slug' : 'texas'
}
},
{
...
},
]
}
before I try to alter it, I at least see if I can access it.
console.log( filter.and[0].term.terms.region.slug );
However, I get:
Uncaught TypeError: Cannot read property 'region' of undefined
Maybe because the interpreter is expecting the dot notation to point to levels of an object, whereas this portion of the json going to ES is...erm.. not an object (although it's referencing an object?) This is where I get confused.
EDIT: For reference, this is what the terms object for a single result looks like in Elasticsearch.
This is because the binding you've used (i.e., 'terms.region.slug') is incompatible with dot-notation. Use of dot-notation requires that the binding be parseable as an identifier. However, bracket notation is equivalent to dot-notation and allows any binding to be used.
console.log( filter.and[0].term['terms.region.slug'] );
Related
This question already has an answer here:
How to access object property beginning with a number (SyntaxError: Unexpected identifier)
(1 answer)
Closed 2 years ago.
I have the following object:
If I try to get the value from it by using let result = object.3h I get the following error
error: `Parsing error: Identifier directly after number`.
Identifiers in Javascript can’t start with a number (You can check the exact rules at the link provided.
When dealing with object properties, you can use string literals for defining properties that won’t follow this rule (Which might also happen when dealing with JSON objects)
In order to access this properties you need to use a property accessor
On your case:
day.rain[‘3h’]
you need to use bracket notation
correct
object["3h"]
incorrect
object.3h
const object = { "3h": 0.44 }
console.log(object["3h"])
This question already has answers here:
JavaScript property access: dot notation vs. brackets?
(17 answers)
Are Javascript arrays primitives? Strings? Objects?
(7 answers)
Closed 2 years ago.
I'm looking for an elegant way of understanding JavaScript array and objects.
I came to an anomaly in which I got stuck.
Since in PHP or other languages, when we make an array e.g
$a = [
admin => 1,
staff => 2
];
so if we want to access its element we can do so by for e.g $a[admin] and we will get 1.
similarly if its an object e.g
$a = (object) [];
$a->sadd = 'sas';
we can access it with arrow
$a->sadd
and if we try to access object elements in the style of array i.e like this $a['sadd'] it will throw error that you can not use it as array style.
But I was surprised by the anomaly in JavaScript.
I have observed that in JavaScript no matter what I am making, an array or object, the elements of both can be accessed via dot or via array style and i found no difference in there accessing style.
for e.g
var a = {sadd : 1}
I can access its element via a['sadd'] or a.sadd both will give 1
So I am confused by this anomaly and wondering whether array and object both datatypes are considered same in JavaScript?
An array is indeed an object.
Javascript is a dynamic language and accepts mixed types of entities. Also while accessing, dot notation seems to be more clearer (atleast imo) and is preferred. Bracket notation is used for dyanamic keys.
The difference between array and objects boils down to their usecase:
Array -> Contiguous block of memory
Object -> key-value pair (like a dictionary)
Your php example is actually creating what we'd call an object in JS, not an array. In JS an array is a list of items, which you can find items by array[i], or by looping.
An object is a collection of fields, which you can go into by object.fieldName or object[fieldName].
This can be confusing in JS though, because theoretically everything is an "object", including arrays, due to the way things are handled lower down..
I would recommend following along with the https://justjavascript.com/ course for good mental models on how objects work in JS.
This question already has answers here:
JavaScript property access: dot notation vs. brackets?
(17 answers)
How can I access object properties containing special characters?
(2 answers)
Closed 5 years ago.
I've got some data that's getting returned from an API and converted into a js object in PHP before being passed back to the browser. One of the values i'm trying to retrieve from this object lives in the objects attributes. Here is what the object structure looks like in JS:
Currently I can access all properties I need to by calling object.comments for example or object.email.whatever.
What I can't do is access the objects attributes. Ideally I would like to get to the ID via something like object.#attributes.id but this returns an error.
Is it possible to access an objects attributes and if so how should I go about it?
Thanks
To access properties using dot notation the property must be a valid identifier. If it's not, you have to use brackets:
object['#attributes'].id
This question already has answers here:
How can I access and process nested objects, arrays, or JSON?
(31 answers)
JavaScript property access: dot notation vs. brackets?
(17 answers)
Closed 8 years ago.
I need to know why this isn't working. My Javascript code accesses a variable in an object. But it appears not to be working, partly because I can't figure out the syntax.
var obj = {
size:"small",
big:false,
thing:true
}
alert(obj[size]);
I'm just not sure if I got the syntax right…
This will work here.
obj.size //returns small
OR
obj["size"] //returns small
OR
var my_var = "size"
obj[my_var] //returns small
You can reference object values either by:
obj["size"]
or
obj.size
However, there is an exception. For instance, if you have following object with a number key: (Note: key is still a string even if it's defined this way):
var obj = {
1: true
};
You can retrieve it's value only by using: obj["1"]
Hence, using obj.1 will cause a syntax error.
Therefore, your code works if you change it to e.g.: alert(obj["size"]); but I prefer to use console.log(obj["size"]); for debugging. At least, if you are playing with node.js as your tags indicates.
Cheers.
This question already has answers here:
Why can't I add properties to a string object in javascript?
(2 answers)
Closed 9 years ago.
Do variables have properties?
The obvious answer should be NO. If I try to assign a property to a variable, it should give an error. Right?
If I do something like:
var someVariable = 'Cat';
someVariable.eyes = 'two'; //Gives no error!
alert(someVariable.eyes); // alerts 'undefined' instead of giving an error!
Variables don't have properties, but their values do. (If the value's an object, anyway.)
In this case, you're trying to set the eyes property of the string currently referenced by someVariable.
It won't work in this case, though. Since primitive values don't have properties, JS will convert the primitive string value into an object and set the property on that object, which pretty much immediately gets silently discarded. The end result: the primitive string remains unmodified.
"Variables" don't actually exist (except strictly within the definition of a scope), only objects. And string objects can't have arbitrary properties assigned by default.