getting wrong values looping through array for a particular value in javascript

Question

I have a function that is supposed to loop through an array and count the values in the array that are true. in the example below, I am expecting a value of 4, since the values 6, 3, 30, and 7 are all truthy values while 0 is false.

function countTruthy(arr) {
 var arrayLength = arr.length;
 var truthy = 0;
 for (var i = 0; i < arrayLength; i++) {
 if(arr[i] == true) {
 truthy++
 }
 }
 
 return console.log(truthy)
}
countTruthy([6, 3, 0, 30, 7])

But the code above doesn't work and I keep getting 0 instead

Answer 1

While all non-zero numbers are truthy, it is not equal to true. Only 1 is equal to true. To double-check this, just try running 60 == true in your console and it will return false, however, if you run if (60) console.log('hi') it will print 'hi'.

tl;dr: Truthy values are not necessarily equal to true.

To fix this, just check if the value is 0 instead. Like this:

function countTruthy(arr) {
 return arr.filter(x => x != 0).length;
}
console.log(countTruthy([6, 3, 0, 30, 7]))

Also, your function can be drastically reduced with .filter(). Just filter out all the zero values then return the length of the resulting array.

Answer 2

Whether a value is "truthy" (like 6 is truthy, but not really equal to true) has a meaning that goes beyond just numbers, and besides 0, also NaN is a falsy value in the numeric data type domain. To accurately count truthy values, you can use Boolean as call back, like this:

const countTruthy = arr => arr.filter(Boolean).length;
console.log(countTruthy([6, 3, 0, 30, 7])); // 4
console.log(countTruthy([6, 3, NaN, 30, 7])); // 4
console.log(countTruthy(["a", "b", "", "c", "d"])); // 4
console.log(countTruthy([true, true, false, true, true])); // 4
console.log(countTruthy([{}, undefined, null])); // 1

Answer 3

As @Michael mentioned above, 0 is false but not all truthy values are equal to true. With that said, here is how you can achieve the desired result.

function countTruthy(arr) {
 var arrayLength = arr.length;
 var truthy = 0;
 for (var i = 0; i < arrayLength; i++) {
 if (arr[i]) {
 truthy += 1;
 }
 }
 return console.log(truthy);
}
countTruthy([6, 3, 0, 30, 7])