一文带你了解JavaScript函数柯里化

function add(a, b) {
    return a + b
}

add(1, 2); // 3

function _add(a){
    return function(b){
        return a + b
    }
}

_add(1)(2);  // 3

// 拼接地址
function getUrl(protocol, hostname, pathname) {
    return `${protocol}${hostname}${pathname}`;
}

const url1 = getUrl('https://', 'www.baidu.com', '/hasa');
const url2 = getUrl('https://', 'www.baidu.com', '/saandsa');
const url3 = getUrl('https://', 'www.baidu.com', '/hasak');

console.log(url1, url2, url3)

function curry(protocol) {
    return function (hostname, pathname) {
        return `${protocol}${hostname}${pathname}`;
    }
}

const url_curry = curry('https://');

const url1 = url_curry('www.baidu.com', '/hasa');
const url2 = url_curry('www.baidu.com', '/saandsa');
const url3 = url_curry('www.baidu.com', '/hasak');

console.log(url1, url2, url3)

/*
* @param    element       Object      DOM元素对象
* @param    type          String      事件类型
* @param    listener      Function    事件处理函数
* @param    useCapture    Boolean     是否捕获
*/
var addEvent = function (element, type, listener, useCapture) {
    if (window.addEventListener) {
        element.addEventListener(type, function (e) {
            listener.call(element, e)
        }, useCapture)
    } else {
        element.attachEvent('on' + type, function (e) {
            listener.call(element, e)
        })
    }
}

var curEvent = (function () {
    if (window.addEventListener) {
        return function (element, type, listener, useCapture) { // return funtion
            element.addEventListener(type, function () {
                listener.call(element)
            }, useCapture)
        }
    } else {
        return function (element, type, listener) {
            element.attachEvent('on' + type, function () {
                listener.call(element)
            })
        }
    }
})

var addEvent = curEvent();
addEvent(element, "click", listener)

let fishWeight = 0;
const addWeight = function(weight) {
    fishWeight += weight;
};

addWeight(2.3);
addWeight(6.5);
addWeight(1.2);
addWeight(2.5);

console.log(fishWeight);

function curryWeight(fn) {
    let _fishWeight = [];
    return function () {
        if (arguments.length === 0) {
            return fn.apply(null, _fishWeight);
        } else {
            _fishWeight = _fishWeight.concat([...arguments]);
        }
    }
}

function addWeight() {
    let fishWeight = 0;
    for (let i = 0, len = arguments.length; i < len; i++) {
        fishWeight += arguments[i];
    }
    return fishWeight;
}

const _addWeight = curryWeight(addWeight);
_addWeight(6.5);
_addWeight(1.2);
_addWeight(2.3);
_addWeight(2.5);
console.log(_addWeight())

function curry() {
    let args = [...arguments];
    let inner = function () {
        args.push(...arguments);
        return inner;
    }
    
    // 核心内容：隐式转换，调用了内部的toString
    inner.toString = function () {
        return args.reduce(function (pre, next) {
            return pre + next;
        })
    }
    return inner;
}

const result = curry(1)(2);
console.log(Number(result));