为什么 Set 对象拆分字符串？

Question

const set = new Set("123");

console.log(set);

输出是“设置{'1','2','3'}”

Answer 1

因为字符串是 iterable, and when you give the Set constructor an iterable object,¹ it loops through the values provided by the object's iterator and adds them to the set. In the case of strings, the string iterator iterates the strings code points — in your example, "1", "2", and "3". (For more about "code points" vs. "code units" and what a string is, read my blog post。）

如果要将字符串添加到集合中，则必须单独添加或将其包装在另一个可迭代对象（如数组）中：

// Add separately:
let set = new Set();
set.add("123");
console.log(set.size); // 1
console.log([...set]); // ["123"]

// Or wrap:
set = new Set(["123"]);
console.log(set.size); // 1
console.log([...set]); // ["123"]

¹（或原始类型，例如强制转换为可迭代对象的字符串）

Answer 2

Set constructor takes an iterable 并获取它的每个值。

字符串 have an @@iterator property by default 使它们可迭代：

const foo = "xyz";

console.log(...foo);

const [a, b, c] = foo;
console.log(a, b, c);

for (const char of foo)
  console.log(char);

因此，这正是将字符串传递给 Set 构造函数时发生的情况 - 它绘制每个值，就像处理任何其他可迭代对象一样：

const foo = "xyz";
const bar = [1, 2, 3]

console.log("set of string:", new Set(foo));
console.log("set of array :", new Set(bar));

<h1>Check the browser console</h1>

为什么 Set 对象拆分字符串？

Why is Set object split string?

javascript

string

set