Question

我有一个在JavaScript中扩展Date对象的小类。一种方法只返回UTC中的当前日期。

Date.prototype.nowUTC = function(options) {

    var now = new Date();

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

我想要做的是将options参数定义为包含小时，分钟和秒的对象，这些对象将被添加到时间中。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，所以在添加或设置默认值之前，我不必检查它是否已定义？（例如function(options = {'hours' : null, 'minutes' : null, 'seconds' : null) {}）我更喜欢将parmeter像 - 作为一个对象 - 而不是为每个值传递单独的参数。

谢谢！

Answer 1

您可以创建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....
};

Answer 2

Object.assign是为对象分配值并使用输入扩展该对象的最简单方法。

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign

所以在您的情况下：

Date.prototype.nowUTC = function(options) {

    var defaults = {
        hours: 0,
        minutes: 0,
        seconds: 0,
    };
    var now = new Date();

    options = Object.assign(defaults, options);

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

定义JavaScript函数参数的对象默认值

2 个答案: