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How to combine array within another array using javascript or jquery?

I have an array named arr and within that array, I have another array.My question is, how to combine this two array?
var arr=["1","2","[3,4]","5"]
My output should be like this:
1,2,3,4,5
Thanks in advance!

You could use spread syntax ... with map and JSON.parse methods.
var arr = ["1","2","[3,4]","5"]
var result = [].concat(...arr.map(e => JSON.parse(e)))
console.log(...result)

Considering that you have an actual array and not a string you can flatten like this
var arr=["1","2",["3","4"],"5"]
var flat = [].concat(...arr)
console.log(flat)

You can change it to string and further replace the square brackets using replace(/[\[|\]]/g,''):
var arr=["1","2","[3,4]","5"];
var res = arr.toString().replace(/[\[|\]]/g,'');
console.log(res);

If the question is how to flat an array like this [1,2,[3,4],5] or this [1,[2,[[3,4],5]]] into this[ 1, 2, 3, 4, 5 ] here a pretty general and short solution:
var arr = [1, [2, [[3, 4], 5]]];
var newArr = JSON.parse("[" + JSON.stringify(arr).replace(/\[|\]/g, "") + "]");
console.log(newArr)
Or .flat if browser supports it:
var arr = [1, 2, [3, 4, [5, 6]]];
arr.flat();
console.log(arr)

Javascript push an array to a 2-dim array

So i have 2 single dim arrays
array1 = [1,2,3];
array2 = [4,5,6];
And an empty 2-dim array
setArray = [[],[]];
How am i going to push the contents of the arrays to setArray so that it looks like this... considering we don't know the length of the single dim arrays?
setArray = [
[1,2,3],
[4,5,6]
];
I'm working on a project and my problem looks like this. Thank you.

if you just want to push contents of the two arrays in setArray you can do something like this:
Each element of setArray will have a reference to one of the arrays.
var array1 = [1,2,3], array2 = [4,5,6];
var setArray = [];
setArray.push(array1);
setArray.push(array2);
console.log(setArray);

array1 = [1,2,3]; array2 = [4,5,6];
setArray = [array1,array2];
console.log(setArray)
You can do it this way too.

how to push an element at index 0 of an array [duplicate]

This question already has answers here:
How to insert an item into an array at a specific index (JavaScript)
(28 answers)
Closed 6 years ago.
i have a situation like this,
i have 2 array1 as array1 = ["fruit","vegetables"];
and
array2 = [["apple","banana"],["tomato"]]; // index 0:represent fruit i,e (["apple","banana"]), index 1: vegetables i,e (["tomato"])
my question : how can i push item from array1 so as to make my array2 look like this
[["fruit","apple","banana"],["vegetables","tomato"]];
with that i can determine index:0 as category.
MY data structure is these 2 array array1 = ["fruit","vegetables"]; AND array2 = [["apple","banana"],["tomato"]];
if i'm able to get key value pair array that would good for me.
my sample data:
array1 = ["fruit","vegetables"];
array2 = [["apple","banana"],["tomato"]]; //expected output :[["fruit","apple","banana"],["vegetables","tomato"]];

Use Array#unshift method.
var array1 = ["fruit", "vegetables"],
array2 = [
["apple", "banana"],
["tomato"]
];
var array3 = array2.map(function(v, i) { // iterate over the array to generate the new array
var arr = v.slice(); // copy the array
arr.unshift(array1[i]) // insert element at beginning
return arr; /// return generated array
});
console.log(array3)
UPDATE : If you don't want to create a new array then you can avoid the copying part.
var array1 = ["fruit", "vegetables"],
array2 = [
["apple", "banana"],
["tomato"]
];
array2.forEach(function(v, i) { // iterate over the array
v.unshift(array1[i]) // insert element at beginning
});
console.log(array2)
With ES6 arrow function :
var array1 = ["fruit", "vegetables"],
array2 = [
["apple", "banana"],
["tomato"]
];
array2.forEach((v, i) => v.unshift(array1[i]));
console.log(array2)

Try this Array.map() and Array.unshift() .unshift() push the data into array [0]index position.
array1 = ["fruit","vegetables"];
array2 = [["apple","banana"],["tomato"]];
array2.map((a,i) => a.unshift(array1[i]))
console.log(array2)

Store result of array.sort in another variable

This seems like a simple question but I can't find much info on this.
var array1 = new Array(4, 3, 1, 2, 0, 5);
var array2 = array1;
array2.sort(function(a, b) {
return a - b;
})
Expected behavior: array2 is sorted and array1 is in the original order starting with 4.
Actual result: both arrays are sorted.
How can I sort array1 - while maintaining array1 and storing the results of the sort in array2? I thought that doing array2 = array1 would copy the variable, not reference it. However, in Firefox's console both arrays appear sorted.

That's becasue with var array2 = array1; you're making a new reference to the object, so any manipulation to array2 will affect array1, since the're basically the same object.
JS doesn't provide a propner clone function/method, so try this widely adopted workarround:
var array1 = new Array(4, 3, 1, 2, 0, 5);
var array2 = JSON.parse(JSON.stringify(array1));
array2.sort(function(a, b) {
return a - b;
});
Hope it helps :)

You can copy a array with slice method
var array1 = new Array(4, 3, 1, 2, 0, 5);
var array2 = array1.slice();

How to use array variable in array?

I have an array and I want to put same array and other array inside of the first array.
var arr=["a","b","c",arr,arr2];
var arr2=["a","b"];
var arr3=[];
arr3=arr[3];
When I print out arr, I can see
["a","b","c",,]
But if I print out arr3, The result is undefined.
How can I fix it?

You need to do this in the right order:
var arr1 = [];
var arr2 = [ "a", "b" ];
// Now arr1 and arr2 are defined so you can throw them into another array:
var arr3 = [ "a", "b", "c", arr1, arr2 ];

You've defined arr as part of itself - arr[3] is arr. But at the time, arr doesn't exist yet, so it comes out as undefined.