Code I can't do without on JS

combine.js

var argsToArr = function (args) {
  return Array.prototype.slice.call(args, 0);
};

var argFn = function (fn) {
  return function () {
    return fn(argsToArr(arguments));
  };
};

exports.curry = function (fn) {
  return argFn(function curried (args) {
    if (args.length >= fn.length) {
      return fn.apply(null, args);
    } else {
      return argFn(function (args2) {
        return curried.apply(null, args.concat(args2));
      });
    }
  });
};

exports.compose = argFn(function (args) {
  if (args.length === 1) {
    return args[0];
  }
  return args.reduce(function (f, g) {
    return function () {
      return f(g.apply(null, arguments));
    };
  });
});


exports.threadFirst = argFn(function (args) {
  return function (initialValue) {
    return args.reduce(function (prev, curr) {
      if (curr instanceof Array) {
        var fn = curr.shift();
        curr.unshift(prev);
        return fn.apply(null, curr);
      } else {
        return curr(prev);
      }
    }, initialValue);
  };
});


exports.threadLast = argFn(function (args) {
  return function (initialValue) {
    return args.reduce(function (prev, curr) {
      if (curr instanceof Array) {
        var fn = curr.shift();
        curr.push(prev);
        return fn.apply(null, curr);
      } else {
        return curr(prev);
      }
    }, initialValue);
  };
});