📘arr.reduce()

// ⭐️ array ---> reduced into a single value
let finalResult = arr.reduce(
  // ⭐️ reducer function
  (prevResult, next, i, array) =>  nextResult,
  // ⭐️ if initial value not provided, `arr[0]` will be used instead,
  //    iteration will start from `arr[1]`.
  [initialValue]
);

🔴 主題

• early break reduce()

💈範例

let value = arr.reduce(function(accumulator, item, index, array) {
  // ...
}, [initial]);

📘 手冊

• Array.prototype ⟩

  • .reduce()

  • .slice() - 擷取某一段，產生新陣列。

  • .splice() - 截斷原陣列、插入新元素。(⭐️ 注意：會回傳「被截掉的部分」❗️)

📗 參考

• JS.info ⟩ reduce(), reduceRight()