# JavaScript: Find all indexes of NaN in an array

## JavaScript Array: Exercise-52 with Solution

Write a JavaScript program to get all the indexes where NaN is found in a given array of numbers and NaN.

Test Data:

([2, NaN, 8, 16, 32]) -> [1]
([2, 4, NaN, 16, 32, NaN]) -> [2,5]
([2, 4, 16, 32]) ->[]

Sample Solution:

JavaScript Code :

``````// Function to find all indexes of NaN in an array
function test(arr_nums){
// Use map to create an array of indexes where NaN is found, otherwise return false
return arr_nums.map(function(el, i){
if(isNaN(el))
return i;
return false;
})
// Use filter to remove falsy values (non-NaN elements)
.filter(function(el){
return el;
});
}

// Test the function with an array containing NaN at multiple indexes
arr_nums = [2, NaN, 8, 16, 32];
console.log("Original array: "+arr_nums);
result = test(arr_nums);
console.log("Find all indexes of NaN in the said array: "+result);

// Test the function with another array containing NaN at multiple indexes
arr_nums = [2, 4, NaN, 16, 32, NaN];
console.log("Original array: "+arr_nums);
result = test(arr_nums);
console.log("Find all indexes of NaN in the said array: "+result);

// Test the function with an array without NaN
arr_nums = [2, 4, 16, 32];
console.log("Original array: "+arr_nums);
result = test(arr_nums);
console.log("Find all indexes of NaN in the said array: "+result);
``````

Output:

```Original array: 2,NaN,8,16,32
Find all indexes of NaN of the said array: 1
Original array: 2,4,NaN,16,32,NaN
Find all indexes of NaN of the said array: 2,5
Original array: 2,4,16,32
Find all indexes of NaN of the said array:
```

Flowchart :

Live Demo :

See the Pen javascript-array-exercise-52 by w3resource (@w3resource) on CodePen.

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