I have both an object and an array:
var elementsArr = [];
var elements = {
polygon: 734,
infoContent: "huhu",
id: 0
}
I am going to have multiple "elements" and push each one into "elementsArr".
for(var i=0; i<20; i++){
elements.id = id +=1;
elementsArr.push(elements);
}
My problem now is how to access a specific "id" within the object elements, within the array elementsArr and pushing this into another array.
I tried this but it doesn't seem to be working:
var ids = [];
for(var m=0; m<elementsArr.length; m++){
if(elements.id == elementsArr[m]){
ids.push(elements.id);
}
How do I do this?
Your code is pushing the same object onto the array over and over again.
One way to fix that would be to write a function to get a new element:
function Element(id) {
return {
polygon: 734,
infoContent: "huhu",
id: id
};
}
for(var i=0; i<20; i++){
elementsArr.push(Element(i));
}
If there are going to be a lot of elements, and the "id" values are all relatively small numbers, you'd be better off storing the elements such that the "id" is also the index:
for (var i = 0; i < 20; i++)
elementsArr[i] = Element(i);
To get the element with "id" 17, then:
var element17 = elementsArr[17];
If you really want to search, however, you can use .find()
:
var element17 = elementsArr.find(function(elem) { return elem.id === 17; });
or a simple loop:
for (var i = 0; i < elementsArr.length; ++i) {
if (elementsArr[i].id === 17) {
// found it!
}
}
You can extract the "id" values from the array with a simple call to .map()
:
var ids = elementsArr.map(function(elem) { return elem.id; });
or another for
loop:
var ids = [];
for (var i = 0; i < elementsArr.length; ++i)
ids.push(elementsArr[i].id);
There are a couple of ways to do this. If you are able to work in ES6
then a WeakMap
would be great.
However, I'm going to give you an ES5
instead.
Option 1 Loop through the data.
If you aren't accessing the data often, then looping through as you've done so may be the best choice.
Option 2 Set up your own index
On the other hand, if you need faster lookup, you can set up your own separate index to look things up.
var elementsLookup = {}; // Create an empty object.
for(var i=0; i<20; i++){
elements.id = id +=1;
elementsLookup[id] = elements; // Stash off a copy
elementsArr.push(elements);
}
Then you can look things up with a
var elem = elementsLookup[2]; // Get the element with an id of 2.
It is easy to do it with Array prototyping. Here is a function findById
Array.prototype.findById = function(id){
for(var x = 0 ; x < this.length; x++){
if(this[x].id == id){
return this[x];
}
}
return false;
}
You can use this function to recieve any id from the array or false if it does not exists
elementsArr.findById(17);
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