javascript delete 数组长度不变

javascript  delete  数组 中的某些数值后，数组的长度是不变的

var a = [1, 2, 3, 4, 5, 6];
for (var i in a) {
    if (a[i] % 2 == 0) {
        delete a[i];
    }
}
console.log(a);
console.log(a.length);