Question

Trying to replicate the Implicit Iterators in Python, using JavaScript my code doesn’t return “Dylan”, despite being a male.

Python:

names = [person.name for person in roster if person.male]

JavaScript Algorithm Test:

roster = {
    person: [
        {
            name: "Katie",
            male: false
        },
        {
            name: "Dylan",
            male: true
        },
        {
            name: "Alex",
            male: true
        },
        {
            name: "John",
            male: true
        }
    ]
}

var names = []
var number = -1

for(var loop = 0; loop < roster.person.length; loop++) {
    if(roster.person[loop].male == true) {
        names[number++] = roster.person[loop].name
    }
}

console.info(names)

>>> [code] Returns –> [“Alex”, “John”]

Why is this? My loop goes through all the values and my if then statement is valid.

Answer 1

That’s because you are trying to insert an element at position -1 of the array. See Increment and decrement operators.

Either use ++number instead of number++:

for(var loop = 0; loop < roster.person.length; loop++) {
    if(roster.person[loop].male == true) {
        names[++number] = roster.person[loop].name
    }
}

Or initialize the variable number to 0 instead of -1, or instead of using a variable to hold the current index value, just use .push, which adds a new element to the array.

Also, you don’t need to explicitly compare with true, it suffices that the expression evaluates to true:

for (var loop = 0; loop < roster.person.length; loop++) {
    if (roster.person[loop].male) {
        names.push(roster.person[loop].name);
    }
}