使用给定的格式字符串返回从字符串解析的日期。

包装在两个单引号字符（'）之间的格式字符串中的字符被转义。 一行中的两个单引号，无论是在引号序列的内部还是外部，都代表“真实”单引号。

格式字符串的格式基于Unicode技术标准＃35：https：//www.unicode.org/reports/tr35/tr35-dates.html#Date_Field_Symbol_Table，其中有一些补充（请参见表格下方的注释5）。

可接受的格式字符串模式：

笔记：

1. 在默认的美国语言环境 中，“格式化”单位（例如，格式化季度）与“独立”单位相同，但在某些语言中有所不同。在日期的上下文中 ，根据语言规则拒绝“格式化”单位 。“独立”单位始终是主格单数。 在功能上，它们将产生不同的结果：format

   format(new Date(2017, 10, 6), 'do LLLL', {locale: cs}) //=> '6. listopad'

   format(new Date(2017, 10, 6), 'do MMMM', {locale: cs}) //=> '6. listopadu'

   parse 将尝试可互换地匹配格式和独立单元。

2. 相同字母的任何序列都是一个模式，除非由 单引号引起来（请参见下文）。 如果序列长于表中所列：

• 对于数字单位（）将尝试匹配与序列一样宽的数字yyyyyyyyparse

• 对于文本单位（）将尝试匹配该单位的最大变体形式。这些变化在表的最后一栏中标记为“ 2”。MMMMMMMMparse

• i：ISO星期几

• I：一年中的ISO周

• R：ISO周编号年份

• o：序数修饰符

值将按照其单位优先级的降序分配给日期。 优先级相同的单元按出现顺序相互覆盖。

如果没有解析更高优先级的值（例如，解析字符串'January 1st'而没有年份），则 这些值将取自第3个参数，该参数用作解析的上下文。baseDate

baseDate必须传递该函数才能正常工作。 如果不确定要提供哪个，请创建一个新的Date实例：在这种情况下，将在当前日期的上下文中进行解析。如果是或者值转换为有效的，那么将被退回。baseDate parse('02/11/2014', 'MM/dd/yyyy', new Date()) baseDateInvalid DateDate Invalid Date

结果可能因地区而异。

如果与匹配但不提供令牌，将返回。formatStringdateStringbaseDate

如果解析失败，将返回。无效日期是一个日期，其时间值为NaN。日期的时间值：http：//es5.github.io/#x15.9.1.1Invalid Date

Return the date parsed from string using the given format string.

The characters in the format string wrapped between two single quotes characters (') are escaped.Two single quotes in a row, whether inside or outside a quoted sequence, represent a 'real' single quote.

Format of the format string is based on Unicode Technical Standard #35:https://www.unicode.org/reports/tr35/tr35-dates.html#Date_Field_Symbol_Table with a few additions (see note 5 below the table).

Accepted format string patterns:

Notes:

1. "Formatting" units (e.g. formatting quarter) in the default en-US locale are the same as "stand-alone" units, but are different in some languages. "Formatting" units are declined according to the rules of the language in the context of a date. "Stand-alone" units are always nominative singular.In format function, they will produce different result:

   format(new Date(2017, 10, 6), 'do LLLL', {locale: cs}) //=> '6. listopad'

   format(new Date(2017, 10, 6), 'do MMMM', {locale: cs}) //=> '6. listopadu'

   parse will try to match both formatting and stand-alone units interchangably.

2. Any sequence of the identical letters is a pattern, unless it is escaped by the single quote characters (see below). If the sequence is longer than listed in table:

• for numerical units (yyyyyyyy) parse will try to match a number as wide as the sequence

• for text units (MMMMMMMM) parse will try to match the widest variation of the unit. These variations are marked with "2" in the last column of the table.

• i: ISO day of week

• I: ISO week of year

• R: ISO week-numbering year

• o: ordinal number modifier

Values will be assigned to the date in the descending order of its unit's priority. Units of an equal priority overwrite each other in the order of appearance.

If no values of higher priority are parsed (e.g. when parsing string 'January 1st' without a year), the values will be taken from 3rd argument baseDate which works as a context of parsing.

baseDate must be passed for correct work of the function. If you're not sure which baseDate to supply, create a new instance of Date: parse('02/11/2014', 'MM/dd/yyyy', new Date()) In this case parsing will be done in the context of the current date. If baseDate is Invalid Date or a value not convertible to valid Date, then Invalid Date will be returned.

The result may vary by locale.

If formatString matches with dateString but does not provides tokens, baseDate will be returned.

If parsing failed, Invalid Date will be returned. Invalid Date is a Date, whose time value is NaN.Time value of Date: http://es5.github.io/#x15.9.1.1