Find index of NaN in a javascript array

Question

[1, 2, 3].indexOf(3) => 2

[1, 2, NaN].indexOf(NaN) => -1

[1, NaN, 3].indexOf(NaN) => -1

Answer 1

You have to look at each item to return an array of the indexes that are NaN values-

function findNaNs(arr){
    return arr.map(function(itm, i){
        if(isNaN(itm)) return i;
        return false;
    }).filter(function(itm){
        return itm;
    });
}

findNaNs([1, NaN, 3, 4, 'cat'/3])

//or to find the first one-

function firstNaN(arr){
    var i= 0, L= arr.length;
    while(i