剩余参数

function sum(...theArgs) {
  let total = 0;
  for (const arg of theArgs) {
    total += arg;
  }
  return total;
}

console.log(sum(1, 2, 3));
// 期望输出：6

console.log(sum(1, 2, 3, 4));
// 期望输出：10

function f(a, b, ...theArgs) {
  // …
}

function myFun(a, b, ...manyMoreArgs) {
  console.log("a", a);
  console.log("b", b);
  console.log("manyMoreArgs", manyMoreArgs);
}

myFun("one", "two", "three", "four", "five", "six");

// 控制台输出：
// a, one
// b, two
// manyMoreArgs, ["three", "four", "five", "six"]

function ignoreFirst(...[, b, c]) {
  return b + c;
}

function wrong1(...one, ...wrong) {}
function wrong2(...wrong, arg2, arg3) {}
function wrong3(...wrong,) {}
function wrong4(...wrong = []) {}

function myFun(a, b, ...manyMoreArgs) {
  console.log("a", a);
  console.log("b", b);
  console.log("manyMoreArgs", manyMoreArgs);
}

myFun("one", "two", "three", "four", "five", "six");

// a, "one"
// b, "two"
// manyMoreArgs, ["three", "four", "five", "six"] <-- 一个数组

// 使用上述示例中同样的函数定义

myFun("one", "two", "three");

// a, "one"
// b, "two"
// manyMoreArgs, ["three"] <-- 具有一个值的数组

// 使用上述示例中同样的函数定义

myFun("one", "two");

// a, "one"
// b, "two"
// manyMoreArgs, [] <-- 还是一个数组

// 使用上述示例中同样的函数定义

myFun("one");

// a, "one"
// b, undefined
// manyMoreArgs, [] <-- 还是一个数组

function fun1(...theArgs) {
  console.log(theArgs.length);
}

fun1(); // 0
fun1(5); // 1
fun1(5, 6, 7); // 3

function multiply(multiplier, ...theArgs) {
  return theArgs.map((element) => multiplier * element);
}

const arr = multiply(2, 15, 25, 42);
console.log(arr); // [30, 50, 84]

function sortRestArgs(...theArgs) {
  const sortedArgs = theArgs.sort();
  return sortedArgs;
}

console.log(sortRestArgs(5, 3, 7, 1)); // 1, 3, 5, 7

function sortArguments() {
  const sortedArgs = arguments.sort();
  return sortedArgs; // 永远不会返回
}

console.log(sortArguments(5, 3, 7, 1));
// 抛出 TypeError（arguments.sort is not a function）

function fn(a, b) {
  const normalArray = Array.prototype.slice.call(arguments);
  // — 或 —
  const normalArray2 = [].slice.call(arguments);
  // — 或 —
  const normalArrayFrom = Array.from(arguments);

  const first = normalArray.shift(); // 没问题，返回第一个参数
  const firstBad = arguments.shift(); // 报错，arguments 不是普通数组
}

function fn(...args) {
  const normalArray = args;
  const first = normalArray.shift(); // 没问题，返回第一个参数
}