How to get value at a specific index of array In JavaScript?
You can access an element at a specific index using the bracket notation accessor.
var valueAtIndex1 = myValues[1];
On newer browsers/JavaScript engines (see browser compatibility here), you can also use the .at()
method on arrays.
var valueAtIndex1 = myValues.at(1);
On positive indexes, both methods work the same (the first one being more common). Array.prototype.at()
however allows you to access elements starting from the end of the array by passing a negative number. Passing -1
will give the last element of the array, passing -2
the second last, etc.
See more details at the MDN documentation.
How to insert an item into an array at a specific index (JavaScript)
You want the splice
function on the native array object.
arr.splice(index, 0, item);
will insert item
into arr
at the specified index
(deleting 0
items first, that is, it's just an insert).
In this example we will create an array and add an element to it into index 2:
var arr = [];
arr[0] = "Jani";
arr[1] = "Hege";
arr[2] = "Stale";
arr[3] = "Kai Jim";
arr[4] = "Borge";
console.log(arr.join()); // Jani,Hege,Stale,Kai Jim,Borge
arr.splice(2, 0, "Lene");
console.log(arr.join()); // Jani,Hege,Lene,Stale,Kai Jim,Borge
Javascript: How to get values of an array at certain index positions
Use Array.map
:
arr = ["a","b","c","d"]
indexes = [0,2]
const res = indexes.map(e => arr[e])
console.log(res)
Javascript getting an array from the index of another array
You could collect all indices in an object with the color as property.
This approach features
a classic
for
statement for iterating the index,a logical nullish assignment
??=
to check the property and assign an array if not given,and
Array#push
, to get the index into the array with the color as name.
const
colors = ['blue', 'red', 'red', 'red', 'blue', 'red', 'blue', 'blue'],
indices = {};
for (let i = 0; i < colors.length; i++) {
(indices[colors[i]] ??= []).push(i);
}
console.log(indices);
how to fetch a value from specific index of object property that has the values of pushed array in javascript
Inside your loop you concatenate all the inputs in one string and push that one string to array.
loop 1: text="0<br>"
loop 2: text="0<br>1<br>"
and so on.
at the end of your loop your text value is "0<br>1<br>2<br>3<br>4<br>5<br>"
and then you push it to array
so when you fetch the index 0 element it returns the string with all values. What you can do is stop concatenating and push each input to array inside the loop
<html>
<body>
<p id="demo"></p>
<script>
try {
let result = {
marks: [], //
};
const n = 5;
let text = "";
for (let i = 0; i < n; i++) {
text = prompt("Enter value of " + i, i) + "<br>";
result.marks.push(text)
}
document.getElementById("demo").innerHTML = result.marks[1]; // it now returns value from specific index.
}
catch (err) {
document.write(err);
};
</script>
</body>
</html>
How do I check in JavaScript if a value exists at a certain array index?
Conceptually, arrays in JavaScript contain array.length
elements, starting with array[0]
up until array[array.length - 1]
. An array element with index i
is defined to be part of the array if i
is between 0
and array.length - 1
inclusive. If i is not in this range it's not in the array.
So by concept, arrays are linear, starting with zero and going to a maximum, without any mechanism for having "gaps" inside that range where no entries exist. To find out if a value exists at a given position index (where index is 0 or a positive integer), you literally just use
if (i >= 0 && i < array.length) {
// it is in array
}
Now, under the hood, JavaScript engines almost certainly won't allocate array space linearly and contiguously like this, as it wouldn't make much sense in a dynamic language and it would be inefficient for certain code. They're probably hash tables or some hybrid mixture of strategies, and undefined ranges of the array probably aren't allocated their own memory. Nonetheless, JavaScript the language wants to present arrays of array.length
n as having n members and they are named 0 to n - 1, and anything in this range is part of the array.
What you probably want, however, is to know if a value in an array is actually something defined - that is, it's not undefined
. Maybe you even want to know if it's defined and not null
. It's possible to add members to an array without ever setting their value: for example, if you add array values by increasing the array.length
property, any new values will be undefined
.
To determine if a given value is something meaningful, or has been defined. That is, not undefined
, or null
:
if (typeof array[index] !== 'undefined') {
or
if (typeof array[index] !== 'undefined' && array[index] !== null) {
Interestingly, because of JavaScript's comparison rules, my last example can be optimised down to this:
if (array[index] != null) {
// The == and != operators consider null equal to only null or undefined
}
How to get an array of values based on an array of indexes?
for(var i = 0; i < indexArr.length; i++)
resultArr.push(fruitier[indexArr[i]]);
javascript array index ascending by value value
Try this one by using array.sort
and array.indexOf
const arr = [4, 6, 1, 3, 5, 0, 2];
const newarr = arr.slice()
const arrindex = []
newarr.sort()
newarr.forEach(i=>{
arrindex.push(arr.indexOf(i))
})
console.log(arrindex)
get value name from array for specific index
Maybe this can help: https://developer.mozilla.org/en-US/docs/Web/API/Window/name
'var name' refers to the global window.name.
this global.name will be converted to a string of you log it to the console. (see output below)
With 'let name' you declares a block-scoped local variable. (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let#:~:text=Description,function%20regardless%20of%20block%20scope.)
How to find the array index with a value?
You can use indexOf
:
var imageList = [100,200,300,400,500];
var index = imageList.indexOf(200); // 1
You will get -1 if it cannot find a value in the array.
Related Topics
How to Detect the Clearing of a "Search" HTML5 Input
How to Get the Title of HTML Page with JavaScript
Good Reasons Why Not to Use Iframes in Page Content
How to Stop User from Printing Webpages? Using JavaScript or Jquery
Bootstrap and Jqueryui Conflict
The Purpose of Starting an Initial Comment with /*! in JavaScript and CSS Files
How to Call a Js Function Using Onclick Event
"Status Code:200 Ok (From Serviceworker)" in Chrome Network Devtools
Dynamically Add CSS to Page via JavaScript
Fix First Column of a Bootstrap Table
How to Get Color Value from Gradient by Percentage with JavaScript
How to Avoid Global Variables in JavaScript
How to Use Jquery with Reactjs