通过实例了解Javascript柯里化流程

function sum(a, b, c) {
 return a + b + c;
}
// 调用
sum(1, 2, 3); // 6

function sum(a) {
 return function (b) {
  return function(c) {
    return a + b + c;
    } 
  }
}
// 调用
let sum1 = sum(1);
let sum2 = sum1(2);
sum2(3); // 6

sum1 = function(b) {
  return function(c) {
  // 注意此时变量a存在于闭包中，可以调用，a = 1
  return a + b + c;
 }
}

sum2 = function(c) {
 // 变量a,b皆在闭包中, a = 1, b = 2
 return a + b + c;
}

function volume(length, width, height) {
  return length * width * height;
}
volume(200, 100, 200);
volume(200, 150, 100);
volume(200, 50, 80);
volume(100, 50, 60);

function volume(length, width, height) {
  return function(width) {
    return function(height) {
     return length * width * height;
      }
  }
}
let len200 = volume(200);
len200(100)(200);
len200(150)(100);
len200(50)(80);
volume(100)(50)(60);

function execOnce(fun) {
  let flag = true;
 return function() {
  if (flag) {
   fun && fun();
   flag = false;
  }
 }
}
let onceConsole = execOnce(function() {
  console.log('只打印一次');
});
onceConsole();
onceConsole();

let onceConsole = function() {
 if (flag) {
    (function() {
    console.log('只打印一次');
   })()
   flag = false;
  }
}

 // 第一版
var curry = function (fn) {
 var args = [].slice.call(arguments, 1);
 return function() {
  var newArgs = args.concat([].slice.call(arguments));
  return fn.apply(null, newArgs);
 };
};
 function add(a, b) {
  return a + b;
 }

var addFun = curry(add, 1, 2);
addFun() // 3
//或者
var addOne = curry(add, 1);

var addFun = curry(function(a, b,c) {
 return a + b + c;
}, 1);
addFun(2)(3); // 报错 addFun(...) is not a function

function curry(fn, args) {
 var length = fn.length;
 args = args || [];
 return function(...rest) {
  var _args = [...args, ...rest];
  return _args.length < length
   ? curry.call(this, fn, _args)
  : fn.apply(this, _args);
 }
}
var fn = curry(function(a, b, c) {
 console.log(a + b + c);
});
fn('a', 'b', 'c'); // abc
fn('a', 'b')('c'); // abc
fn('a')('b')('c'); // abc