Return the total number of matching pairs of numbers

matching-pairs.js

function numberPairs(n, ar) {
    if (n !== ar.length) {
        console.error('Invalid array length');
    }

    const obj = {};
    const pairs = [];
    const pairsLength = 0;

    do {
        const temp = ar.shift();

        if (!obj[temp]) {
            obj[temp] = 1;
        } else {
            obj[temp]++;
            if (obj[temp] === 2) {
                pairs.push(temp);
                obj[temp] = 0;
            }
        }
    } while (ar.length);

    console.log(pairs);
    console.log(obj);
  
    return pairs.length;
}

numberPairs(9, [10, 20, 20, 10, 10, 30, 50, 10, 20]);