如何使用map在每个数组元素的末尾添加文本？ [英] How to add text to end of each array element using map?

问题描述

我正在尝试编写一个映射到数组的函数，并将一串文本添加到数组中每个元素的末尾。当我执行console.log时，我只会得到 undefined 。任何帮助将不胜感激。

I am trying to write a function that maps over an array and add a string of text to the end of each element in the array. When I do a console.log I just get undefined. Any help would be greatly appreciated.

这里是数组：

let arr = ["England","Scotland","Westeros"];

这就是我要尝试的：

dragonMapper = (arr) => {
  let newArr = arr.map(function(e) {
    e += '...here be dragons'
  });
  return newArr;
}

console.log(dragonMapper(newArr));

这是我希望函数执行后的数组：

This is what I want the array to be after the function is executed:

["England...here be dragons","Scotland...here be dragons","Westeros...here be dragons"];

推荐答案

.map 的回调函数期望返回值

.map's callback function expects a return value

let arr = ["England", "Scotland", "Westeros"];

dragonMapper = arr => {
  let newArr = arr.map(function(e) {
    return e + '...here be dragons'; //Return the concatenated value of 2 strings
  });
  return newArr;
}

console.log(dragonMapper(arr));

更短版本，带有箭头函数语法：

Shorter version, with the arrow function syntax:

let arr = ["England", "Scotland", "Westeros"];

dragonMapper = arr => {
  return arr.map(e => e + '...here be dragons');
}

console.log(dragonMapper(arr));

这篇关于如何使用map在每个数组元素的末尾添加文本？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！