I might be wrong , but curious to know whether can i construct an object with key value pair, with value accepting space only
Somehow after parsing i need to get as
properties:
name:
value: //accepting space
let property = { name: {'value':} }; //currently its giving me error like expression expected
I need to give something like this , is it possible in js or in react
Any help will be highly appreciated
You can create objects with undefined or null values, like this:
let property = {
name: undefined,
value: undefined
}
let null_property = {
name: null,
value: null
}
which is the closest you can get to 'empty space' in Javascript, if you mean what I think you mean.
You can't, however, not assign anything at all in your syntax because Javascript requires that something be assigned to every single variable. You can test this by noting that:
let thing;
and
let thing = undefined;
are the EXACT same line of code from your computer's perspective. The first is simply a convenient shorthand way to write the second.
Related
// My input String
// Could be on : true, on : false, bri : 255, etc, etc
var inputString = 'on : true'
console.log(inputString);
var wrongResult = { inputString }
console.log(wrongResult);
// The result that I am trying to achieve
var desiredResult = {
on : true
}
console.log(desiredResult);
Run it: https://repl.it/LCDt/4
I created the above code snippet to demonstrate the problem that I am experiencing. I have an input string that I receive that could be "on : true", "on : false", "bri : 250", "sat : 13", etc. When posting this data to a server, the format that works is seen above as the "desireResult".
But, when taking a string, such as 'on : true', in a variable, and placing it inside {}, it always seems to create a dictionary with the variable name as the key and the string itself as the value.
Can someone explain why this is and how to get around it?
Can someone explain why this is
Because the syntax { foo } means "Create an object, give it a property called foo, give that property the value of the foo variable.
how to get around it
Parse the data. Assign it explicitly.
Start by splitting the string on :. Then remove the white space. Then test is the second value is a number or a keyword. And so on.
This would be easier if the data you were receiving was in a standard format. Then you could use an existing parser. If you have control over the input: Change it to be valid JSON and then use JSON.parse.
You could use JSON.parse for that but you need to feed him valid JSON.
You need to have an string in form of:
{"on":true}
using JSON.parse('{"on":true}') will return you the desired object.
I have a variable called uids
var uids = [];
Then I write some value to it property
uids[16778923] = "3fd6335d-b0e4-4d77-b304-d30c651ed509"
But before it
if (!uids[user.id]) {
uids[user.id] = generateKey(user);
}
This thing behaves ok. If I try to get the value of it property
uids[currentUser.id]
It will give me a value of this property. If I try to call some methods like
Object.keys(uids);
It will give me, what I expected. And here the mystery comes...
uids;
RAM rest in piece. See the node eating ram
I am very confused now. What's wrong?
This is because you are creating a huge array and node will reserve memory for it - who knows what comes. I'd say that's a scenario where you would use a Map (or a plain object, but Map feels better here.
var uids = new Map();
var key = 456464564564654;
if (! uids.has(key)) {
uids.set(key, generateKey(user))
}
You are creating an empty array (length is zero), then you assign some value to an arbitrary index. This will make the array grow as big as the index and assign the value to that index. Look at this example using node.js REPL:
> var a = []
undefined
> a[5] = "something"
'something'
> a
[ , , , , , 'something' ]
> a.length
6
Instead of creating an array, you could create a Map() or an common javascript object (singleton). Javascript objects behave like Maps but only Strings can be used as keys. If you assign a Number to be key, javascript will convert it to String automatically.
Personally, I would go with objects because they perform better. Instantiating an object takes longer than instantiating a Map (and it doesn't seem like you need to create several groups of "uids"), but once done, adding new keys and retrieving values from any key in faster when using common objects. At least that's how things go in my node.js v6.7.0 on ubuntu 14.04 but you could try for yourself. And it would also make the least alteration to your code.
var uids = {} // common/ordinary empty javascript object instead of array.
if (!uids[user.id]) { // getting value from one key works the same.
uids[user.id] = generateKey(user) // assignment works the same.
}
////
uids[16778923] = "3fd6335d-b0e4-4d77-b304-d30c651ed509" // key will be "16778923".
uids[16778923] // getting value for key "16778923" can be done using 16778923 instead of "16778923".
////
uids[currentUser.id] // still returning values like this.
Object.keys(uids) // still returning an array of keys like this. but they are all Strings.
This is an odd thing to ask I am aware, but I am very much a newbie and can't seem to wrap my head around this. I have a Javascript object sent to me via firebase that looks like this:
var blob = {
matt#email,com: { //notice the comma because periods are illegal in keys
email: "matt#email.com" //actual email with period
name: "Matt Sanford"
pic: "https://lh3.googleusercontent.com/-LeQrq-_KjJE/AAAAAAAAAAI/AAAAAAAAAoI/4l6r2HNdock/photo.jpg"
provider: "google"
uid: "0000000000000000"
}
}
}
I am trying to access the inner most tree via the console like so: console.log(blob.matt#email,com) //throws an error because of an invalid token
even though it should return the object with email, name, etc.
However when I tried the same structure like so:
var blob = {foo: {bar: true} }
console.log(blob.foo) //output '{bar: true}'
There are two things I am wondering, is having the initial key with the modified email illegal because of the commas or is there not a way to read such a key in javascript? Recommendations are appreciated because I am just learning as I go along here.
Update
How would I go about accessing the keys dynamically? Clearly it would be impossible to input each key dynamically. How would I read it without knowing what exactly the key name is?
What you posted is not a json object, it's a javascript object. JSON would have all its keys quoted.
Comma's are definitely allowed, but you cannot use the standard obj.property syntax like this:
console.log(blob.matt#email,com)
You must do:
console.log(blob['matt#email,com']);
This is a fairly common question here in SO, and I've looked into quite a few of them before deciding to ask this question.
I have a function, hereby called CheckObjectConsistency which receives a single parameter, an object of the following syntax:
objEntry:
{
objCheck: anotherObject,
properties: [
{
//PropertyValue: (integer,string,double,whatever), //this won't work.
PropertyName: string,
ifDefined: function,
ifUndefined: function
}
,...
]
}
What this function does is... considering the given parameter is correctly designed, it gets the objCheck contained within it (var chk = objEntry.objCheck;), It then procedes to check if it contains the properties contained in this collection.
Like this
for(x=0;x<=properties.length;x++){
if(objCheck.hasOwnProperty(properties[x].PropertyName)){
properties[x].ifDefined();
}
else{
properties[x].ifUndefined();
}
What I want is... I want to bring it to yet another level of dynamicity: Given the propositions that IfDefined and IfUndefined are functions to be called, respectively, if the currently-pointed PropertyName exists, and otherwise, I want to call these functions while providing them, as parameters, the very objCheck.PropertyName's value, so that it can be treated before returning to the user.
I'll give a usage example:
I will feed this function an object I received from an external provider (say, a foreign JSON-returning-WebService) from which I know a few properties that may or may not be defined.
For example, this object can be either:
var userData1 = {
userID : 1
userName: "JoffreyBaratheon",
cargo: "King",
age: 12,
motherID : 2,
//fatherID: 5,--Not defined
Status: Alive
}
or
var userData2 = {
userID :
userName: "Gendry",
cargo: "Forger Apprentice",
//age: 35, -- Not Defined
//motherID: 4,-- Not Defined
fatherID: 3,
Status: Alive
}
My function will receive:
var objEntry=
{
objCheck: userData1,
properties: [
{
PropertyName: "age",
ifDefined: function(val){alert("He/she has an age defined, it's "+val+" !");},
ifUndefined: function(){alert("He/she does not have an age defined, so we're assuming 20.");},
},
{
PropertyName: "fatherID",
ifDefined: function(val){alert("He/she has a known father, his ID is "+val+" !");},
ifUndefined: function(){alert("Oh, phooey, we don't (blink!blink!) know who his father is!");},
}
]
}
CheckObjectConsistency(objEntry); // Will alert twice, saying that Joffrey's age is 12, and that his father is supposedly unknown.
ifDefined will only actually work if, instead of properties[x].ifDefined();, I somehow provide it with properties[x].ifDefined(PropertyValue);. And here, at last, lies my question.
Being inside the consistency-checking-function, I only know a given property's name if it's provided. Being inside it, I can't simply call it's value, since there is no such function as properties[x].ifUndefined(properties[x].GetValueFromProperty(properties[x].PropertyName)) ,... is there?
I'm sorry. Not being a native english speaker (I'm brazilian), I can't properly express my doubts in a short way, so I prefer to take my time writing a long text, in an (hopefully not wasted) attempt to make it clearer.
If, even so, my doubt is unclear, please let me know.
I think you're looking for the bracket notation here. It allows you to provide an arbitrary value as key to access the object. Also, you know its name. You have your properties object right?
objEntry.properties.forEach(function(property){
// Check if objCheck has a property with name given by PropertyName
if(!objEntry.objCheck.hasOwnProperty(property.PropertyName)){
// If it doesn't, call isUndefined
property.isUndefined();
} else {
// If it does, call isDefined and passing it the value
// Note the bracket notation, allowing us to provide an arbitrary key
// provided by a variable value to access objCheck which in this case is
// the value of PropertyName
property.isDefined(objEntry.objCheck[property.PropertyName]);
}
});
Oh yeah, forEach is a method of arrays which allows you to loop over them. You can still do the same with regular loops though.
I have this code:
var string = {
nameString : "nameValue",
nameString2 : "nameValue2",
nameString3 : "nameValue3",
datathing : 0,
};
var data = {
data : 1,
dataNum2 : 2,
dataNum3 : 3,
dataNum4 : 4,
};
var thing = {
datathing1 : 10,
datathing2 : 20,
datathing3 : 30,
datathing4 : 40,
};
var object = {
object1 : string,
data1 : data,
thing1 : thing,
};
Why do neither of these means to access the data work:
alert("testReference= " + object['object1']['string']['nameString']);
alert("testReference= " + object.object1.string.nameString);
I cannot understand it, even though similar examples found below and textbooks state explicitly that they should work:
Accessing nested JavaScript objects with string key
Thanks in advance for any input!
I am currently constructing an object and passing it around, a 'for in' will bring up the values but a 'typeof' test or any other way I try and access will not work, either I will encounter an error (which breaks the program, I think) or I get 'undefined'....
One last thing if this gets solved, is it ok to nest a key that is the same name value as its parent, such as data.data - this leads to the possibility of further nesting such as data.data.data...
Let's look at what's wrong with each example, then take a look at the way that works right.
Example 1
object['object1']['string']['nameString']
We expect object['object1'] to return the object string, right? So lets simplify the big expression by replacing that part of it. That'll make it easier for us to understand.
So now we have string['string']['nameString'].
But string has no member called 'string', so string['string'] returns undefined.
And when you try to treat undefined as an object, you get an error!
Example 2
object.object1.string.nameString
We expect object.object1 returns the object string, right? So lets simplify the big expression by replacing that part of it. That'll make it easier for us to understand.
So now we have string.string.nameString.
But string has no member called 'string', so string.string returns undefined.
And when you try to treat undefined as an object, you get an error!.
What You Want
object.object1.nameString (or object['object1']['nameString'])
We expect object.object1 returns the object string, right? So lets simplify the big expression by replacing that part of it. That'll make it easier for us to understand.
So now we have string.nameString, and we expect that to return "nameValue".
And it does!