JavaScript concat不能按预期的方式工作，关心详细说明？ [英] JavaScript concat not working as expected, care to elaborate?

问题描述

所以，我有这个对象包含国家名称作为关键，值是一些城市的阵列。我想把所有的城市都排成一列，没有国家。这是我如何去做，不明白为什么它不工作：

pre c $ c $ var city = {
英国：['london']，
西班牙：['ibiza'，'malaga']，
USA：['hollywood']
}

var allCities = [];
（城市c）{
allCities.concat（城市[c]）;
}
console.log（allCities）; //给出空数组

如果我替换 allCities.concat（cities [c ]） with console.log（cities [c]）我得到所有这样的数组：

  ['london'] 
 ['ibiza'，'malaga'] 
 ['hollywood'] 
  

这就是我的挫折感来自何处。任何想法，为什么这是行不通的？

解决方案

根据 Array.prototype.concat ：

返回由此数组与其他数组
和/或值（s）组成的新数组。 $ b

这意味着它不会修改它应用到的对象。

更改为：

  allCities = allCities.concat（cities [ C]）; 
  

So, I have this object containing country names as keys and the values are arrays with some cities. I want to get all the cities in one array, without the countries. Here's how I go about it and can't understand why it isn't working:

var cities = {
    "United Kingdom": ['london'],
    "Spain": ['ibiza', 'malaga'],
    "USA": ['hollywood']
}

var allCities = [];
for (c in cities) {
    allCities.concat(cities[c]);
}
console.log(allCities); //gives empty array

If I replace allCities.concat(cities[c]) with console.log(cities[c]) I get all the arrays like this:

['london']
['ibiza', 'malaga']
['hollywood']

So that's where my frustration comes from. Any idea why this isn't working?

解决方案

As per documentation of Array.prototype.concat:

Returns a new array comprised of this array joined with other array(s) and/or value(s).

Which means it does not modify the object it is applied to.

Change to:

allCities = allCities.concat(cities[c]);

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