JavaScript: Find all indexes of NaN in an array

JavaScript Array: Exercise-52 with Solution

Find NaN Indexes in Array

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.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that iterates over an array and collects all indexes where the element is NaN.
• Write a JavaScript function that uses isNaN() to identify NaN values and returns their positions in an array.
• Write a JavaScript function that properly handles sparse arrays and returns an empty array if no NaN is found.
• Write a JavaScript function that validates the input and returns an array of indices where NaN values occur.

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