9.Rest Parameter.html

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  <!-- take a variable number of arguments.
            取可变数量的参数。
            allows us to apply map(), filter() and reduce() on the parameters array.
            允许我们在参数数组上应用map()、filter()和reduce()。
    -->
  <script>
    // 放置在形参上面的是不定参数
    function howMany(...args) {
      return "You have passed " + args.length + " arguments.";
    }
    console.log(howMany(0, 1, 2)); // You have passed 3 arguments.
    console.log(howMany("string", null, [1, 2, 3], {})); // You have passed 4 arguments.


    const sum = (x, y, z) => {
      const args = [x, y, z];
      return args.reduce((a, b) => a + b, 0);
    }

    const sum2 = (...args) => {
      const args1 = args;
      return args1.reduce((a, b) => a + b, 0);
    }
    console.log(sum(1, 2, 3)); // 6
    console.log(sum2(1, 2, 3)); // 6
  </script>
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