SOURCE

let currying = function(fn){
  let stored_args = [].slice.call(arguments,1);
  console.log(stored_args);//截取第一个参数
  return function(){
    let args = stored_args.concat([].slice.call(arguments));
    return fn.apply(null,args);
  }
}

function add(x,y){
  return x+y;
}

let result = currying(add,5)(2);
console.log(result);//7