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📜  Prototype-枚举

📅  最后修改于: 2020-10-21 08:46:30             🧑  作者: Mango

 

Enumerable类为枚举提供了大量有用的方法。枚举是充当值集合的对象。

枚举方法主要用于枚举数组和哈希。还有其他对象，例如ObjectRange和各种与DOM或AJAX相关的对象，您可以在其中使用枚举方法。

上下文参数

每个带有迭代器的Enumerable方法都将上下文对象作为下一个(可选)参数。上下文对象是迭代器要绑定的对象，因此其内部的this关键字将指向该对象。

var myObject = {};

['foo', 'bar', 'baz'].each(function(name, index) {
   this[name] = index;
}, myObject); // we have specified the context

myObject;

这将产生以下结果-

输出

{ foo: 0, bar: 1, baz: 2}

有效使用

  • 当需要在所有元素上调用相同的方法时，请使用invoke()方法。
  • 当需要在所有元素上获取相同的属性时，请使用pluck()方法。
  • findAll / select方法检索与给定谓词匹配的所有元素。相反， reject()方法将检索与谓词不匹配的所有元素。在需要两个集合的特定情况下，可以避免循环两次：只需使用partition()方法。

这是与Enumerable相关的所有方法的完整列表。

Prototype可枚举方法

注意-确保您至少具有1.6版的prototype.js。

S.No. Method & Description
1. all()

Determines whether all the elements are boolean-equivalent to true, either directly or through computation by the provided iterator.
2. any()

Determines whether at least one element is boolean-equivalent to true, either directly or through computation by the provided iterator.
3. collect()

Returns the results of applying the iterator to each element. Aliased as map().
4. detect()

Finds the first element for which the iterator returns true. Aliased by the find() method.
5. each()

It lets you iterate over all the elements in a generic fashion, then returns the Enumerable, thereby allowing chain-calling.
6. eachSlice()

Groups items in chunks based on a given size, with last chunk being possibly smaller.
7. entries()

Alias for the more generic toArray method.
8. find()

Finds the first element for which the iterator returns true. Convenience alias for detect().
9. findAll()

Returns all the elements for which the iterator returned true. Aliased as select().
10. grep()

Returns all the elements that match the filter. If an iterator is provided, it is used to produce the returned value for each selected element.
11. inGroupsOf()

Groups items in fixed-size chunks, using a specific value to fill up the last chunk if necessary.
12. include()

Determines whether a given object is in the Enumerable or not, based on the == comparison operator. Aliased as member().
13. inject()

Incrementally builds a result value based on the successive results of the iterator.
14. invoke()

Optimization for a common use-case of each() or collect(): invoking the same method, with the same potential arguments, for all the elements.
15. map()

Returns the results of applying the iterator to each element. Convenience alias for collect().
16. max()

Returns the maximum element (or element-based computation), or undefined if the enumeration is empty. Elements are either compared directly, or by first applying the iterator and comparing returned values.
17. member()

Determines whether a given object is in the Enumerable or not, based on the == comparison operator. Convenience alias for include().
18. min()

Returns the minimum element (or element-based computation), or undefined if the enumeration is empty. Elements are either compared directly, or by first applying the iterator and comparing returned values.
19. partition()

Partitions the elements in two groups: those regarded as true, and those considered false.
20. pluck()

Optimization for a common use-case of collect(): fetching the same property for all the elements. Returns the property values.
21. reject()

Returns all the elements for which the iterator returned false.
22. select()

Alias for the findAll() method.
23. size()

Returns the size of the enumeration.
24. sortBy()

Provides a custom-sorted view of the elements based on the criteria computed, for each element, by the iterator.
25. toArray()

Returns an Array representation of the enumeration. Aliased as entries().
26. zip()

Zips together (think of the zip on a pair of trousers) 2 + sequences, providing an array of tuples. Each tuple contains one value per original sequence.