javascript - 为 JavaScript 函数参数定义对象默认值

Question

我有一个小类可以扩展 JavaScript 中的 Date 对象。一种方法仅以 UTC 格式返回当前日期。

Date.prototype.nowUTC = function(options) {

    var now = new Date();

    return new Date(now.getUTCFullYear(), 
                    now.getUTCMonth(), 
                    now.getUTCDate(), 
                    now.getUTCHours(), 
                    now.getUTCMinutes(), 
                    now.getUTCSeconds());
}

我想做的是将选项参数定义为一个包含小时、分钟和秒的对象，并将其添加到时间中。例如，

Date.prototype.nowUTC = function(options) {

    var now = new Date();

    return new Date(now.getUTCFullYear(), 
                    now.getUTCMonth(), 
                    now.getUTCDate(), 
                    now.getUTCHours() + options.hours, 
                    now.getUTCMinutes() + options.minutes, 
                    now.getUTCSeconds()) + options.seconds;
}

有没有办法预先定义这些值，这样我就不必在添加或设置默认值之前检查它是否已定义？ (例如 function(options = {'hours' : null, 'minutes' : null, 'seconds' : null) {})我更喜欢像处理参数一样 - 作为一个对象 - 而不是为每个值传递单独的参数。

谢谢!

Answer 1

您可以制作一个小迭代器来检查对象属性:

Date.prototype.nowUTC = function(options) {

    // Object holding default values for this function
    var defaults = {
      "hours": <default>,
      "minutes": <default>,
      "seconds": <default>
    };

    // Iterate over the options and set defaults where the property isn't defined.
    for (var prop in defaults)  {
      options[prop] = options[prop] || defaults[prop];

      // Note: if options would contain some falsy values, you should check for undefined instead.
      // The above version is nicer and shorter, but would fail if, for example, 
      //    options.boolVal = false
      //    defaults.boolVal = true
      // the defaults would always overwrite the falsy input property.
      options[prop] = typeof options[prop] !== 'undefined' ? options[prop] : defaults[prop];
    }

    var now = new Date();
    // Rest of your function, using the options object....
};