实现一下 call、apply、bind

Function.prototype.mCall = function (obj, ...args) {
  const nObj = typeof obj === 'undefined' ? globalThis : Object(obj);
  const fn = this;
  const key = Symbol();
  nObj[key] = fn;
  const result = nObj[key](...args);
  delete nObj[key];

  return result;
};

function foo(a, b) {
  console.log(this);
  console.log(a, b);
}

foo.mCall(1, 2, 3);

Function.prototype.mApply = function (obj, args) {
  const nObj = typeof obj === 'undefined' ? globalThis : Object(obj);
  const fn = this;
  const key = Symbol();
  nObj[key] = fn;
  const result = nObj[key](...args);
  delete nObj[key];

  return result;
};

foo.mApply(1, [2, 3]);

Function.prototype.mBind = function (obj, ...args1) {
  const nObj = typeof obj === 'undefined' ? globalThis : Object(obj);
  const fn = this;
  const key = Symbol();
  nObj[key] = fn;

  return function (...args2) {
    const nArgs = [...args1, ...args2];
    const result = nObj[key](...nArgs);
    delete nObj[key];
    return result;
  };
};

const foo2 = foo.mBind(1, 2, 3);
foo2(4, 5);