柯里化~~

f(a,b,c) → f(a)(b)(c) // 部分函数调用 f(a,b,c) → f(a)(b,c) / f(a,b)(c)

// 没有保存调用时的this
function currying(fn, ...args) {
      if (args.length >= fn.length) {
        return fn(...args);
      } else {
        return (...args2) => currying(fn, ...args, ...args2);
      }
 }
// 保存下this
function curry(fn) {
  const ctx = this;
  function inner(...args) {
    if (args.length === fn.length) return fn.call(ctx, ...args);
    return (...innerArgs) => inner.call(ctx, ...args, ...innerArgs);
  }

  return inner;
}

// test
function test(a, b, c) {
  console.log(a, b, c);
}
const f1 = curry(test)(1);
const f2 = f1(2);
f2(3);


// test
function test(a, b, c) {
  console.log(a, b, c);
}

const f1 = curry(test)(1,2);
// const f2 = f1(2);
f1(3);