empty array & Array.from

empty array bug

    const duplicationArray = (arr = [], times = 2, debug = false) => {
        let result = [];
        let temps = new Array(times);
        console.log(`temps =`, temps);
        temps.forEach(
            (item, i) => {
                // undefined bug
                console.log(`item =`, item);
                let temp = arr;
                result.concat(temp);
                console.log(`result =`, result);
            }
        );
        // for (let i = 0; i < times; i++) {
        //     let temp = arr;
        //     result.concat(temp);
        // }
        if (debug) {
            console.log(`result =`, result.length);
        }
        return result;
    };

solution

Array.from()

bug

let temps = new Array(3);
// (3) [empty × 3]
temps.forEach(
    (item, i) => {
        // empty & undefined bug
        console.log(`item =`, item, i);
    }
);

OK

let temps = Array.from(new Array(3));
// (3) [undefined, undefined, undefined]
temps.forEach(
    (item, i) => {
        // undefined ok
        console.log(`item =`, item, i);
        // item = undefined 0
    }
);