For loop -vs- Map

I got asked last week about getting the index of an object in an array which had the earliest date, so that this array:

let objArr = [
    {
        "date": "2011-08-12T20:17:46.384Z"
    }, {
        "date": "2012-08-12T20:17:46.384Z"
    }, {
        "date": "2013-08-12T20:17:46.384Z"
    }, {
        "date": "2014-08-12T20:17:46.384Z"
    }, {
        "date": "2010-08-12T20:17:46.384Z"
    }, {
        "date": "2009-08-12T20:17:46.384Z"
    }
];

Produces 5 as that element has the earliest day.

I pondered using map but then decided to go all old school and used a for loop like this:

let boringParse = i => parseInt(moment.utc(i.date).format("x"), 10);
let forLoopInt = objA => {
    let min, i, objALength = objA.length;
    for (let y = 0; y < objALength; y++) {
        let now = boringParse(objA[y])
        if (!min || now < min) {
            min = now, i = y;
        }
    }
    return i;
};

Once I got back to my desk I decided to talk it over with James and came up with this:

let boringParse = i => parseInt(moment.utc(i.date).format("x"), 10);
let mapOne = objA => {
    let datesArr = objA.map(boringParse);
    return datesArr.indexOf(Math.min(...datesArr));
};

Turns out that the for loop is the faster, but only just!