This question already has answers here:
Transforming a Javascript iterable into an array
(8 answers)
Closed 2 years ago.
I want to be able to quickly get the entry set from a map. But the entries function returns an iterator. That's not what I want. Sure, I could write a function to iterate through the entries and build it up into an entry set, but it would be much nicer to have my function say:
return map.entries();
instead of
return buildEntriesArray(map);
It doesn't seem like there's a clean way to code around the iterator problem other than wrap it in a bunch of decorated calls for the various inconsistent Iterator/entry set API cruft.
let a = [["foo.com", 32], ["bar.foo.com", 12]];
let m = new Map(a);
// add to map, etc.
let entries = Object.entries(Object.fromEntries(m.entries()));
How can I make it cleaner?
let entries = Array.from(m.entries());
Related
This question already has answers here:
Why Array.indexOf doesn't find identical looking objects
(8 answers)
Closed 3 years ago.
I'm wondering what the best way to determine the membership of one array in another array in JS.
Here's an example
let a = [];
a.push([1,2]);
a.includes([1,2]) <- evaluates to false
a.indexOf([1,2]) <- evaluates to -1
What's the deal here? Any efficient work around?
At the moment, your search array doesn't actually equal the array within your a array as they have 2 different references in memory. However, you could convert your arrays to strings, such that your search can equal another string array within your array.
To do this you could convert your inner arrays to string using .map(JSON.stringify) and then search for the string version of your array using .includes(JSON.stringify(search_arrr)).
See example below:
let a = [];
let search = [1, 2];
a.push([1,2]);
a = a.map(JSON.stringify)
console.log(a.includes(JSON.stringify(search)));
This question already has answers here:
From an array of objects, extract value of a property as array
(24 answers)
Closed 3 years ago.
I have a JSON object in a JavaScript function:
[{"PMID":31206477,"MemberID":1287,"recID":6352},
{"PMID":31202264,"MemberID":1245,"recID":5974},
{"PMID":31201299,"MemberID":1184,"recID":3012},
{"PMID":31196160,"MemberID":1241,"recID":3833}]
That is saved to an Multi-dimensional Array
Is there a better way that I can make a make a new Array with only the PMID element without looping and building it. I know that this question is close to a duplicate but I'm not interested in a merge or a concat. Currently I'm doing
var newArray = [];
for (var i = 0; i < this.pmidList.length; i++) {
newArray.push(this.pmidList[i]["PMID"]);
}
This question maybe a duplicate but if the average person can't find it based upon the title then it should not be considered a duplicate. The solution is the same but the question titles are much different.
You can use the Array.map function.
const input = [{"PMID":31206477,"MemberID":1287,"recID":6352},
{"PMID":31202264,"MemberID":1245,"recID":5974},
{"PMID":31201299,"MemberID":1184,"recID":3012},
{"PMID":31196160,"MemberID":1241,"recID":3833}];
const output = input.map(item => item.PMID);
Documentation
This question already has answers here:
Find object by id in an array of JavaScript objects
(36 answers)
Closed 7 years ago.
I get an array of objects from the backend as this one, currently only three elements but in the future will be more.
[{"code":"lng.dropdown.home","text":"Inicio"},
{"code":"lng.dropdown.shop","text":"Tienda"},
{"code":"lng.button.support","text":"Soporte"}]
What is the most efficient way in javascript to find an element in this array by code, and return the text associated? Can we use lambdas expresions here?
you can use array filter to find the nested object(s) that matches your code property:
var arr =
[{"code":"lng.dropdown.home","text":"Inicio"},
{"code":"lng.dropdown.shop","text":"Tienda"},
{"code":"lng.button.support","text":"Soporte"}];
var res = arr.filter(function(x){
return x.code == 'lng.dropdown.home'
})
console.log(res[0])
[].filter returns an array with the objects that return true inside the callback.
As far as efficiency is concerned for loop are proved to be faster but using higher order methods you earn abstraction .
When not using other libraries, I usually map then find the indexOf, as follows:
data[data.map(function(a){ return a.code }).indexOf("code I am trying to find")];
This returns the element of data at the index where code matches the code you're trying to find.
When I have lodash as a dependency, I usually just do this however:
_.find(data, {code:"code I am trying to find"})
(I think that's the proper syntax)
Edit:
Didn't realize you were already using JQuery, the answer using $.grep is probably best.
This question already has answers here:
dynamic array names javascript
(7 answers)
Closed 7 years ago.
I haven't found an answer to this question on the site. How would I dynamically name arrays in javascript? I need to generate a number of arrays, the number of which is determined at run time. I am trying to make separate ajax requests that sends individual arrays to a php script for processing.
I have come up with this but it does not work:
var 'objectArray'+id = [];
The typical way would be to have an array of arrays.
var arrayOfArrays = [];
arrayOfArrays[id] = []; // add sub array
What you're asking for is a form of dynamic scoping and JavaScript does not support it. You can call the compiler and eval it but that's a pretty bad idea.
Easiest thing is just creating an object and setting them in it
var objectArrays = {};
objectArrays[id] = [];
The way to do literally what you want is finding the scope you're currently in and setting it in it or using eval.
A good way is to use an array of arrays as suggested:
var objectArray = [];
objectArray[id] = [];
If you do not want to use your own array, you can use window object which holds the window global vars in order to store it there as a value as a global var (not a good practice though):
window["objectArray" + id] = [];
Finally, a (bad in this case) alternative way of doing it is by using eval (which is a way to evaluate an expression at runtine in JavaScript in a sense):
eval("var objectArray" + id + " = [];");
This question already has answers here:
Picking 2 random elements from array
(10 answers)
Closed 7 years ago.
I have an array such as:
array=['a','b','c','d','e','f'];
I want to delete a random 2 elements. How can I do this?
To get two unique items from the array, and if you don't mind mutating the original array, you can use splice() to remove the selected item from the array so it won't be picked when you run it a second time:
var firstRandomChoice = array.splice(Math.floor(Math.random()*array.length), 1);
var secondRandomChoice = array.splice(Math.floor(Math.random()*array.length), 1);
If you use a utility library such as lodash, you may already have a function available to do this for you. For example, lodash provides sample(). So if you were using lodash, you could just do something like this to get an array of two random items:
var results = _.sample(array, 2);