尝试自定义平面图 es2017 Javascript 时遗留的数组

Question

I am getting a left over array when trying to use reduce and concat to implement a custom flatmap. I have to use use the reduce concat combo as flatmap does not work in es2017 as i am required to use es2017.

my code:

function flat(object) {
    return Object
        .entries(object)
        .reduce((acc,[k, v]) => acc.concat([k, ...v.map((s) => `${s} ${k}`)]));
}

var data = { message: { arctic: [], atlantic: ["north", "south"], indian: [], pacific: ["north", "south"], southern: [] } },
    result = { message: flat(data.message) };

console.log(result);

my results:

{
message:(10) [
"arctic",
 [],
"atlantic",
"north atlantic",
"south atlantic",
"indian",
"pacific",
"north pacific",
"south pacific",
"southern"
]
}

What I need:

{
message:(9) [
"arctic",
"atlantic",
"north atlantic",
"south atlantic",
"indian",
"pacific",
"north pacific",
"south pacific",
"southern"
]
}

Answer 1

You need to pass an initial value of an empty array to reduce , else the first value of the acc in the reduce will be the first entry of the object (and the first entry of the object is ['arctic', []] . But you want all key-value pairs to have the mapping logic (of concatenating the key, and then concatenating any values the key's array may have) applied to them, you don't want to exclude the first item:

 function flat(object) { return Object.entries(object).reduce((acc, [k, v]) => acc.concat([k, ...v.map((s) => `${s} ${k}`)]), []); // ---------------------------> ^^ } var data = { message: { arctic: [], atlantic: ["north", "south"], indian: [], pacific: ["north", "south"], southern: [] } }, result = { message: flat(data.message) }; console.log(result);