func.call(thisArg, arg1, arg2, ...)
// thisArg為在 func 函數(shù)運(yùn)行時(shí)使用的 this 值
// arg1, arg2等為指定的參數(shù)列表
// 其返回值為調(diào)用有指定 this 值和參數(shù)的函數(shù)的結(jié)果

Function.prototype.call = function (thisArg, ...argsArray) {
  if (typeof this !== "function") {
    throw new TypeError(
      "Function.prototype.call was called on which is not a function"
    );
  }

  if (thisArg === undefined || thisArg === null) {
    thisArg = window;
  } else {
    thisArg = Object(thisArg);
  }

  // 將 func 放入 thisArg 內(nèi)，這樣在調(diào)用 thisArg[func] 時(shí) this 自然就指向了 thisArg
  const func = Symbol("func");
  thisArg[func] = this;

  let result;

  if (argsArray.length) {
    result = thisArg[func](...argsArray);
  } else {
    result = thisArg[func]();
  }

  delete thisArg[func];

  return result;
};

func.apply(thisArg, [argsArray]);
// thisArg為在 func 函數(shù)運(yùn)行時(shí)使用的 this 值
// arg1, arg2等為指定的參數(shù)列表
// 其返回值為調(diào)用有指定 this 值和參數(shù)的函數(shù)的結(jié)果

Function.prototype.apply = function (thisArg, argsArray) {
  if (typeof this !== "function") {
    throw new TypeError(
      "Function.prototype.apply was called on which is not a function"
    );
  }

  if (thisArg === undefined || thisArg === null) {
    thisArg = window;
  } else {
    thisArg = Object(thisArg);
  }

  // 將 func 放入 thisArg 內(nèi)，這樣在調(diào)用 thisArg[func] 時(shí) this 自然就指向了 thisArg
  const func = Symbol("func");
  thisArg[func] = this;

  let result;

  if (argsArray && typeof argsArray === "object" && "length" in argsArray) {
    // 此處使用 Array.from 包裹讓其支持形如 { length: 1, 0: 1 } 這樣的類數(shù)組對(duì)象，直接對(duì) argsArray 展開將會(huì)執(zhí)行出錯(cuò)
    result = thisArg[func](...Array.from(argsArray));
  } else if (argsArray === undefined || argsArray === null) {
    result = thisArg[func]();
  } else {
    throw new TypeError("CreateListFromArrayLike called on non-object");
  }
  delete thisArg[func];
  return result;
};

func.bind(thisArg[, arg1[, arg2[, ...]]])
// thisArg 為調(diào)用綁定函數(shù)時(shí)作為 this 參數(shù)傳遞給目標(biāo)函數(shù)的值， 如果使用 new 運(yùn)算符構(gòu)造綁定函數(shù)，忽略該值
// arg1, arg2為當(dāng)目標(biāo)函數(shù)被調(diào)用時(shí)，被預(yù)置入綁定函數(shù)的參數(shù)列表中的參數(shù)。
// 其返回值為一個(gè)原函數(shù)的拷貝，并擁有指定的 this 值和初始參數(shù)

Function.prototype.bind = function (thisArg, ...argsArray) {
  if (typeof this !== "function") {
    throw new TypeError(
      "Function.prototype.bind was called on which is not a function"
    );
  }
  if (thisArg === undefined || thisArg === null) {
    thisArg = window;
  } else {
    thisArg = Object(thisArg);
  }
  const func = this;
  const bound = function (...boundArgsArray) {
    let isNew = false;

    // 如果 func 不是構(gòu)造器，直接使用 instanceof 將出錯(cuò)，所以需要用 try...catch 包裹
    try {
      isNew = this instanceof func;
    } catch (error) {}

    return func.apply(isNew ? this : thisArg, argsArray.concat(boundArgsArray));
  };

  const Empty = function () {};
  Empty.prototype = this.prototype;
  bound.prototype = new Empty();

  return bound;
};