I have an array which I want stay the same until I say otherwise. How do I prevent it from changing?
var orgArr = [[1,1], [2,2]];
function modArr(arr){
arr[0][0] = 5;
return arr;
}
modArr(orgArr);
console.log(orgArr); // It has changed
https://jsfiddle.net/50e6k7mc/
I tried some with immutable (which I added to the fiddle).
Something like
var orgArr = Immutable.List([[1,1],[2,2]])
Then using toArray(). But I cant get it to work.
In your modifying function you need to convert first from Immutable , modify and then convert back to Immutable
arr=arr.toArray();
//.... modify arr
//....
arr= arr.fromJS(arr);
here is the updated code :
https://jsfiddle.net/zvhp5k91/
Related
I'm new to JavaScript and feel like I must be missing something fundamental here!
I'm creating a function which sorts a list of integers list and returns the minimum value listSort[0].
function sortNumber(a,b) {
return a - b;
}
var min = function(list){
console.log(list[0]);
var listSort = list.sort(sortNumber);
console.log(list[0]);
console.log(listSort[0]);
return list[0];
}
Can anyone explain why the value of list[0] changes after list.sort(sortNumber) is assigned to listSort ?
Thanks!
The sort() function directly changes the array to which is applied. For example:
myArray.sort();
directly changes the content of myArray.
If you do not want to change the content of the original array you need to use a cloning function:
function mySortingFunction(list){
var newList = myCloningFunction(list);
newList.sort();
return newList;
}
There are several ways to clone an array:
Javascript fastest way to duplicate an Array - slice vs for loop
If you use AngularJS you can simply write:
var newList = angular.copy(list);
To get the minimum value of an Array, better use Math.min
var list = [4,2,4,2,6,5,2,4,3,5,2];
var min = Math.min.apply(null, list);
If i'm right, it's because when you use your assignment, you are executing list.sort(sortNumber) and so list change as per the assignment function.
Sooo... read like this :
- list.sort(sortNumber) => List change
- list is assigned to listSort
Despite this fact, I think you're going to far to find the min value. :P
I am creating an array like the following:
var arr =[];
arr['key1'] = 'value1';
arr['key2'] = 'value2';
If is use this array in ng-repeat tag, it is not displaying anything. Is there any way to make it work?
<div data-ng-repeat='(key,value) in arr'>{{key}} - {{value}}</div>
Is there any way to make it work?
The way to go, is to creat plain object (instead of array)
// instead of creatin of an Array
// $scope.myArr = [];
// we just create plain object
$scope.myArr = {};
...
// here we just add properties (key/value)
$scope.myArr['attempt1'] = {};
...
// which is in this case same as this syntax
$scope.myArr.attempt1 = {};
Thee is updated plunker
Check more details what is behind for example here:
Javascript: Understanding Objects vs Arrays and When to Use Them. [Part 1]
Your associative array is nothing but an object, as far as JavaScript is concerned. IMO Associative arrays and Objects are almost same.
Ex: Your arr['key1'] = 'value1'; can be called as console.log(arr.key1);
To make your code work, you need to change the array declaration by removing [] and replacing with {} (Curly braces)
Like this var arr = {};
I want to get the features from my layer. So I'm requesting WMSGetFeatureInfo method after a successful request for GetFeatureInfo on my layer.
The returned object is structured like this:
I can read values like BEVDICHTE with var bevdichte = features.BEVDICHTE and so on.
But when I want to get the value of the_geom with var the_geom = features.the_geom it returns an object. Yes it is nested so this is intended but my question is how to get the value ol.geom.MultiPoint
from the_geom?
EDIT:
Unfortunately var target = features.the_geom['actualEventTarget_']; will just return another 'actualEventTarget_' object. This is because the the_geom object is nested into infinity. I attached another screenshot to describe my problem. There are many more nested eventTargets following. Yet I was not able to get the property ol.geom.MultiPolygon.
To access a nested array, just use brackets: '[ ]'
var nestedArray = [[1,2], [3,4]];
var nestedArrayValue = nestedArray[0][0];
// --> returns 1
With your example:
var target = features.the_geom['actualEventTarget_']
By the way, from the looks of it var the_geom = features.the_geom doesn't seem like an array. It has keys, mapped to a value, are you sure this is an array, not an object?
I am trying to create number of arrays like _temp0[],_temp1[],_temp2[] so on and I want to store values of data[] in it.
so value of data[0] goes in array_temp0[] after splitting,
data[1] goes in _temp1[] and so on
to elaborate more-
If value of data[0] is string a,b,c
then array _temp0[] should be
_temp0[0]=a
_temp0[1]=b
_temp0[2]=c
I wrote this function
for(var k=0;k<data.length-1;k++)
{
window['_temp' + k] = new Array();
alert("actual data -- >"+data[k]);
'_temp'+k= data[k].split(',');
alert("data after split -- >"_temp[k]);
}
but it is not working, how do I solve it?
You can do the same using javascript objects. Here is an example of how to do it.
Create an object of name '_temp':
var _temp = {};
When you iterate through 'data' variable then, you can dynamically add attributes to it,say _temp['data0'], _temp['data1'] etc, and every attribute will be an array. For that, you need to write something like:
for(var k=0;k<data.length-1;k++)
{
_temp['data'+k] = data[k].split(',');
}
This will not create the variables identical to what you want. However, this is similar to what you want.
used
window['_temp'+k]= data[k].split(',');
instead of
'_temp'+k= data[k].split(',');
and it worked, thanks to go-oleg
I have the following javascript code:
var objectArray = [];
var allInputObjects = [];
var allSelectObjects = [];
var allTextAreaObjects = [];
//following returns 3 objects
allInputObjects = document.getElementById("divPage0").getElementsByTagName("INPUT");
//following returns 1 object
allSelectObjects = document.getElementById("divPage1").getElementsByTagName("SELECT");
//following returns 0 objects
allTextAreaObjects = document.getElementById("divPage2").getElementsByTagName("TEXTAREA");
//and following statement does not work
objectArray = allInputObjects.concat(allSelectObjects);
And my problem is that the last line is throwing an error.
I tried the above code in Firefox and it says allInputObjects.concat is not a function.
Any clues, I believe the script is not treating allInputObjects as an Array!
Any help will be appreciated.
getElementsByTagName returns a NodeList, which is similar to an Array except that it does not support all those prototype functions.
To seamlessly convert such an array-like object into an Array, use:
var arr = Array.prototype.slice.call(somenodelist, 0);
arr will almost be identical, except that it now has the Array prototype functions supported, like concat.
What the function actually does is returning a partial Array containing the elements of somenodelist, to be precise everything from index 0 and after. Obviously, this are just all elements, therefore this is a trick to convert array-like objects into real Arrays.
Why do you think that allSelectObjects is an array?
It is initially assigned to an empty array, sure. But then it's overwritten by the getElementsByTagName call on line 6(ish). Variables in Javascript are not strongly typed, so the initial assignment does not force later assignments to also be arrays.
I suspect you'll have some type of NodeList or similar, rather than an array, in the variable when you invoke the final line. (That's what's returned by the method in Firefox, at least.)
As Andezej has pointed out, you're not dealing with an array here, you're dealing with a kind of node list.
Here's one way you can create an array to work with based on the result of getElementsByTagName
var tags = obj.getElementsByTagName('input');
for (var j=0;j<tags.length;j++) {
resultArray.push(tags[j]);
}
Just another funny way to convert your NodeList to an array:
var tags = obj.getElementsByTagName('input'),
tags2Arr = (
function toArr(i){
return i ? toArr(i-1).concat(tags[i]) : [tags[0]];
}(tags.length-1)
);
Now if you add a method to the Array.prototype:
Array.prototype.clone = function() {
var arr = this;
return (function clone(i){
return i ? clone(i-1).concat(arr[i]) : [arr[0]];
})(this.length-1);
};
You can convert a NodeList to an array, using this oneliner:
Array.prototype.clone.call(obj.getElementsByTagName('input'));