如何根据出生日期计算年龄

function calculateAge(birthDate) {
  var currentDate = new Date();
  var ageDiff = currentDate - birthDate;
  var ageDate = new Date(ageDiff);
  var age = Math.abs(ageDate.getUTCFullYear() - 1970);
  return age;
}

// 使用示例
var birthDate = new Date("1990-01-01");
var age = calculateAge(birthDate);
console.log("年龄：" + age + "岁");