call、apply、bind模拟实现

call 方法模拟实现

Function.prototype.call = function(context, ...args) {
  var context;
  try {
    context = context || window;
  } catch (e) {
    context = global;
  }
  context.fn = this;
  const result = context.fn(...args);
  delete context.fn;
  return result;
};

apply 方法模拟实现

Function.prototype.apply = function(context, args) {
  var context;
  try {
    context = context || window;
  } catch (e) {
    context = global;
  }
  context.fn = this;
  const result = context.fn(...args);
  delete context.fn;
  return result;
};

bind 方法模拟实现

if (typeof Function.prototype.bind !== 'function') {
  Function.prototype.bind = function(context, ...rest) {
    if (typeof this !== 'function') {
      throw new TypeError('invalid invoked!');
    }
    let self = this;
    return function F(...args) {
      if (this instanceof F) {
        return new self(...rest, ...args);
      }
      return self.apply(context, rest.concat(args));
    };
  };
}