map()函数内部的索引 [英] Index inside map() function
问题描述
我缺少一个选项,它使用 List
从<$ c获取 map
函数中的索引号$ c> Immutable.js :
var list2 = list1.map(mapper => {a:mapper .a,b:mapper.index ???})。toList();
Documentation shows map()
返回 Iterable< number,M>
。有没有什么优雅的方式来满足我需要的?
您将能够获得当前迭代 index
为
另请参阅:: https://developer.mozilla.org/ docs / Web / JavaScript / Reference / Global_Objects / Array / map
$ b
参数
callback -
产生新数组元素的函数,带三个参数:
1)currentValue
当前在数组中处理的元素。
2)索引
索引在数组中处理当前元素。
<3>数组
调用数组映射。
var list = ['h','e','l','l ','o'];
list.map((currElement,index)=> {
console.log(Current iteration is:+ index);
console.log(当前元素是: + currElement);
console.log(\ n);
return'X';
});
输出:
当前迭代为:0
当前元素为:h
当前迭代为:1
当前元素是:e
当前迭代是:2
当前元素是:l
当前的迭代是:3
当前元素是:l
当前迭代是:4
当前元素是:o
I am missing a option how to get the index number inside the map
function using List
from Immutable.js
:
var list2 = list1.map(mapper => { a: mapper.a, b: mapper.index??? }).toList();
Documentation shows that map()
returns Iterable<number, M>
. Is there any elegant way to what I need?
You will be able to get the current iteration index
for the map
API through its 2nd parameter.
See also: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Array/map
Parameters
callback - Function that produces an element of the new Array, taking three arguments:
1) currentValue
The current element being processed in the array.2) index
The index of the current element being processed in the array.3) array
The array map was called upon.
Example:
var list = [ 'h', 'e', 'l', 'l', 'o'];
list.map((currElement, index) => {
console.log("The current iteration is: " + index);
console.log("The current element is: " + currElement);
console.log("\n");
return 'X';
});
Output:
The current iteration is: 0
The current element is: hThe current iteration is: 1
The current element is: eThe current iteration is: 2
The current element is: lThe current iteration is: 3
The current element is: lThe current iteration is: 4
The current element is: o
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