This question already has answers here:
Accessing an object property with a dynamically-computed name
(19 answers)
Closed 6 years ago.
I am not sure how to accurately describe this issue, but the code should suffice. This code is in React.js, but I think it is a JavaScript question more than anything. I have a variable initialization:
const key = this.state.key;
This will evaluate to one of three strings...title, author, or year.
How can I use this variable in the following block?
let filteredBooks = books.filter(
(book) => {
return book.key.toString().toLowerCase().indexOf(this.state.query) !== -1;
}
);
Book has properties title, author, and year... that I want to query, and I would rather not switch through the possible values of key(only 3 right now), in case I want to scale with more properties for the book object later. How can I dynamically reference key, and render it on the fly to either title, author, year, or any other property that key might be. (key is not a property of book). I have tried book.eval(key), but this throws an "undefined is not a function" compilation error at eval(key). Once again, I am using React.js but I am thinking this is a general Javascript question. Thanks!
book[key] is the correct answer posted by Answer Li and Keith in the comments!
Related
This question already has answers here:
How to execute a JavaScript function when I have its name as a string
(36 answers)
Closed 2 years ago.
My problem is simple and I couldn't find the proper answer in this forum. My bad...
I want to do that :
const dataReceived = foo;
foo(state);
How can I do that?
I read it is better to avoid eval, and I couldn't get success with new Function.
Thanks for your help!
EDIT
Thanks for your answers.
I work with React.
In my reducer, I have a create_item case.
I can reach action.category, that can be the word 'currency' or 'country'.
What I want to do is to launch either the method createCurrency or createCountry according what is inside action.category.
That's why I tried to join 'create' and 'action.category' to create a dynamic function name.
But it seems to be a poor idea...
The simplest approach is to create an object which contains an entry where:
the key is a string
the value is a function.
Example:
const myObject = {
myFunction: () => { [... DO SOMETHING...] }
}
Subsequently you will be able to invoke the function, using:
myObject.myFunction();
The above becomes more powerful when you use brackets notation.
Example:
const myString = 'myFunction';
myObject[myString]();
This question already has answers here:
Is it possible to add dynamically named properties to JavaScript object?
(20 answers)
Closed 2 years ago.
I have looked all over google and i have found nothing that fits my needs. How would you add an item to an object. I basically have a string variable that i want as the key. Therefore i cant use obj.key = 'something';. I sort of want it like:
obj = {'somekey': 'somevalue'};
obj.add('someotherkey': 'someothervalue');
console.log(obj);
by obj.add() i mean someone's solution
and then console says {'somekey': 'somevalue', 'someotherkey': 'someothervalue'}
Does anyone know a way to do this. I don't care at what position it is just whether it is there. By the way i'm using node if that helps. If you have any questions on my code please ask.
Very simple:
obj["somekey"] = "somevalue";
You can also use a variable instead:
let myVariable = "somekey";
obj[myVariable] = "somevalue";
Or you just use normal object notation:
obj.somekey = "somevalue"
This question already has an answer here:
How do I access an object property dynamically using a variable in JavaScript?
(1 answer)
Closed 5 years ago.
Testing my ability to write code in JavaScript and Node (perhaps a bit of a monumental effort) and also attempting to understand standards.
I want to dynamically change an attribute in an object as in this examnple:
var parms = {
host:'',
port:'',
user:'',
pass:''
};
parms.user='foo';
parms.pass='bar';
console.log(parms.user);
setParm = function(param,value){
parms.param = value;
}
setParm('user','baz');
console.log(parms.user);
However, I'm completely blind. I feel as though I may be in a blind alley in terms of what I think is possible versus what is actually workable.
You are passing the property as a string, so accessing with . won't work. One solution I know is that you can use dict-like indexing:
var parms = {
host:'',
port:'',
user:'',
pass:''
};
parms.user='foo';
parms.pass='bar';
console.log(parms.user);
setParm = function(param,value){
parms[param] = value;
}
setParm('user','baz');
console.log(parms.user);
This question already has answers here:
Accessing an object property with a dynamically-computed name
(19 answers)
Closed 6 years ago.
I have an object with some data inside. The first level of data are 2 arrays (body, cause). Each body and cause array have arrays inside of them (date, year).
totals:[{body:[
{date:[54,9,3,17]},
{year:[437,61,31,140]}]},
{cause:[
{date:[54,9,3,17]},
{year:[437,61,31,140]}]
}]
What I would like to do is access the body/cause array dynamically based on something the user has changed.
This is how I am accessing them now.
totals[isCause].body[isYear].date[filterNumber]);
My issues is body and date are hard coded in there, and I would like to have access to either body/cause date/year. I can't seem to find what these property names are stored as. I tried to set up a var and do something like this
var bodyCause = "body";
Then I tried to pass it back into my retriever statement.
totals[isCause].bodyCause[isYear].date[filterNumber]);
But that fails. So I'm just trying to figure out what that property name is stored as and if I can dynamically set it when I need to retrieve information.
Your attempt was almost correct. You can easyly use var bodyCause = "body"; and access the content dynamically. Instead of this
totals[isCause].bodyCause[isYear].date[filterNumber]);
you should use this
totals[isCause][bodyCause][isYear].date[filterNumber]);
Should fix your problem.
This question already has answers here:
"Variable" variables in JavaScript
(9 answers)
Closed 9 years ago.
I can't figure out how to use the name of a variable previously created with eval, without knowing it.
I mean:
function getName(menu_name, level){
eval("var menu_"+level+"="+menu_name);
}
Now how do I get the name of the variable I just created? Probably keep using eval, but I have to put that name into a $.post call as one of my field name.
Thanks in advice.
If level is an integer, you can treat it as a numerical index for an array:
var menu = [];
menu[level] = menu_name;
If level is anything else, you can treat it as a key for a dictionary/associative array:
var menu = {};
menu[level] = menu_name;
Then, for either of the solutions, if you want to access your menu_name, simply call menu[level].