javascript find leap year

A leap year refers to a year with a leap day (i.e. February 29) in the Gregorian calendar. According to the rules of the Gregorian calendar, there is a leap every four years, but there is no leap every 100 years and another leap every 400 years. In JavaScript, you can use the following function to find out whether a year is a leap year:

function isLeapYear(year) {
  return (year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0);
}

In the above code, we first determine whether the year is divisible by 4, if it can and is not divisible by 100, or it can be divisible by 400 Divisible, it means this year is a leap year. If the conditions are not met, it is not a leap year.

The implementation of this function is relatively simple, but there are some things that need to be paid attention to. For example, if the parameter passed in when calling a function is not an integer type, there may be problems with the calculation process. In order to avoid this situation, we can add code to check the parameter type at the beginning of the function:

function isLeapYear(year) {
  if (typeof year !== 'number' || year % 1 !== 0) {
    throw new TypeError('Year must be an integer');
  }

  return (year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0);
}

In the above code, we add a parameter type checking logic at the beginning. If the parameter passed in is not an integer type, a type error exception will be thrown. This can improve the robustness of the code and prevent some unpredictable errors.

In addition to checking parameter types, we can also perform some additional optimizations on functions. For example, some caching mechanisms can be added to avoid repeated calculations for the same year. This can save computing resources and improve function performance. The following is a sample code to add a caching mechanism:

function createLeapYearChecker() {
  const cache = {};

  return function(year) {
    if (typeof year !== 'number' || year % 1 !== 0) {
      throw new TypeError('Year must be an integer');
    }

    if (year in cache) {
      return cache[year];
    }

    const isLeapYear = (year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0);
    cache[year] = isLeapYear;
    return isLeapYear;
  };
}

const isLeapYear = createLeapYearChecker();
console.log(isLeapYear(2020)); // true
console.log(isLeapYear(2021)); // false
console.log(isLeapYear(2022)); // false
console.log(isLeapYear(2023)); // false
console.log(isLeapYear(2024)); // true
console.log(isLeapYear(2020)); // true - result is retrieved from cache

In the above code, we changed the original function into a factory function. This factory function returns an inner function, which contains a cache object to store the calculation results. This inner function can receive the year parameter and will first check whether the calculation result of this year already exists in the cache. If it exists, the result stored in the cache is returned directly, otherwise it is calculated again and the result is stored in the cache.

By adding a caching mechanism, we can avoid repeated calculations of the same year when calling the function, which improves the execution efficiency of the function. At the same time, since the caching mechanism is transparent to external code, users do not need additional code to manage the cache.

In short, the problem of finding leap years in JavaScript is a very basic problem, but there may be some things that need attention in actual coding. In addition to the basic judgment logic, we can also optimize functions by adding caching mechanisms and other methods to improve the robustness and execution efficiency of the code.

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