typescript中[location.nlc，…groups]的用途是什么？

我正在学习打字脚本，而且对它非常陌生。目前，我正在尝试阅读一些项目代码，以便能够更快地理解。
我对

[location.nlc，…groups]

和const

nlc

的用法感到困惑。说

groups=['b'，'c'，'d']；
location.nlc=“a”

下面的代码将创建一个具有相同值和键“a”、“b”、“c”、“d”的字典。我的猜测正确吗

const groups = location.groups ? location.groups.split(",") : [];
    const clusters: ClusterMap = {};
    for (const nlc of [location.nlc, ...groups]) {
      clusters[nlc] = nlc;
    }

这是一个带注释的示例，这里有一些整洁的TypeScript功能：

// if the loc.groups has a value, split it by comma (otherwise use an empty array)
const groups = loc.groups ? loc.groups.split(",") : [];

// variable for the cluster map
const clusters: ClusterMap = {};

// for each string (nlc) in the expanded array of loc.nlc (which is 'z'), and all the items in groups (which are a, b, c, d)
for (const nlc of [loc.nlc, ...groups]) {
    // add the item to the cluster map with a key of (for example 'z')
    // and a value of (for exmaple 'z')
    clusters[nlc] = nlc;
}

最终结果是：

{
    z: 'z',
    a: 'a',
    b: 'b',
    c: 'c',
    d: 'd'
}

示例中最酷的功能：

const arr1 = [1, 2, 3];
const arr2 = [4, 5, 6];

// 0,1,2,3,4,5,6
const combined = [0, ...arr1, ...arr2]

或许可以阅读新的es6运营商和功能？