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                <!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />





                function _curry2(fn) {
  return function f2(a, b) {
    switch (arguments.length) {
      case 0:
        return f2
      case 1:
        return _curry1(function(_b) {
          // 将参数从右到左依次赋值 1 2 第一次执行时,是 fn(a, 1)
          return fn(a, _b)
        // 参数长度是 2 时 直接进行计算
        return fn(a, b)

function _curry1(fn) {
  return function f1(a) {
    // 对参数长度进行判断
    if (arguments.length === 0) {
      return f1
    } else {
      // 通过 apply 来返回函数 fn(a, 1)
      return fn.apply(this, arguments)

const add = _curry2(function add(a, b) {
  return Number(a) + Number(b)

// 第一次调用是 fn(a, 1)
let r1 = add(1)

// 第二次调用是 fn(2,1)
let r2 = r1(2)

console.log('result', r2)