摘要：也放出地址，上面有完整工程以及在線演示地址相關(guān)閱讀教學(xué)向行代碼教你實現(xiàn)一個低配版的庫原理篇教學(xué)向行代碼教你實現(xiàn)一個低配版的庫代碼篇教學(xué)向再加行代碼教你實現(xiàn)一個低配版的庫設(shè)計篇教學(xué)向再加行代碼教你實現(xiàn)一個低配版的庫原理篇

書接上一篇： 150行代碼教你實現(xiàn)一個低配版的MVVM庫（1）- 原理篇

為了便于分模塊，和閱讀，我使用了Typescript來進(jìn)行coding，總行數(shù)是正好150行，最早寫DEMO的時候用了ES2015，代碼行數(shù)應(yīng)該在100行出頭，如果你不會搭ts+webpack的編譯UMD環(huán)境，你也可以把本文中的ts語法人肉轉(zhuǎn)成es6或者es2015，我相信這對你（一個有志于學(xué)寫mvvm庫的青年）來說沒有什么難度。

作為作者呢，雖然最后我會放出源碼的地址，你可以去github上掃一眼代碼，但我還是希望你們可以跟我一起，打開個文本編輯器，一個模塊一個模塊把代碼人肉敲出來，這樣的感覺是不一樣的，就好比是你可能之前就閱讀過angular，vue的源碼，但你現(xiàn)在還不是在讀我的文章么？

還是再上一遍設(shè)計圖

設(shè)計的類不多，一共就5個

//SegmentFault.ts
export let SegmentFault = class SegmentFault {
    private viewModelPool = {};   //用來維護(hù)viewModel的別名alias與viewModel之間的關(guān)系
    private viewViewModelMap = {};//用來維護(hù)viewModel和被綁定的view之間的關(guān)系
    public registerViewModel(alias:string, vm:object) {};//在sf正式運作之前我們先要注冊一個下viewModel并給他起一個別名
    public init() {};  //sf庫開始運作的入口函數(shù)
    
    public refresh(alias:string){}; // 暴露一個強制刷新整個viewModel的方法，因為畢竟有你監(jiān)控不到的角落
}

SegmentFault是對用戶暴露的唯一的對象，就像Angular他會暴露一個angular對象給用戶使用一樣。
最終，用戶會這樣來操作SF以達(dá)到雙向綁定的目的
不妨再看看使用效果

有沒有覺得SF的API干凈利落，清新爽潔！

根據(jù)設(shè)計圖的Step 1，先給已注冊的viewModel加上監(jiān)視，這里我們需要一個Watcher類

export class Watcher {
    private sf;
    
    //構(gòu)造函數(shù)里傳入一個sf的對象，便于callback調(diào)用時的作用域確定。。。這是后話
    constructor(sf) {
        this.sf = sf;
    }
    public observe(viewModel, callback) {} //暗中觀察
}

再來看一下Step 2, 另一個主要的類Scanner，Scanner是干什么的呢？作用就一個遍歷整個DOM Tree把出現(xiàn)sf-xxxx這個attribute的Elements全部挑出來，然后找sf-xxxx = expression，等號右邊這個表達(dá)式里如果出現(xiàn)了viewModel的alias，那就說么這個element是跟viewModel搭界了，是綁定在一起了，scanner負(fù)責(zé)把這對"戀人"關(guān)系用一個數(shù)據(jù)結(jié)構(gòu)維護(hù)一下，等全部掃描完了一起返回給SegmentFault去聽候發(fā)落。

//Scanner.ts
export class Scanner {

    private prefix = "sf-"; //庫的前綴
    private viewModelPool;
    
    constructor(viewModelPool) {
        this.viewModelPool = viewModelPool; //Scanner肯定是為SegmentFault服務(wù)的，所以初始化的時候SegmentFault會把之前注冊過的viewModel信息傳給Scanner，便于它去掃描。
    }
    
    public scanBindDOM():object {} //找出attribute里帶sf-，且等號右邊表達(dá)式里含有viewModel的alias的Element，并返回一個view與viewModel的map

}

接下去，SegmentFault會獲得Scanner.scanBindDOM()所返回的view_viewModel Map,來看看這個Map的具體數(shù)據(jù)結(jié)構(gòu)

//template
{
    "vm_alias":[
        {
            "viewModel":viewModel,
            "element":element,
            "expression":expression,
            "attributeName":attributeName
        }
    ]
}
//如果實際中的DOM Tree是這樣的，

    

    

//那么，Scanner掃描到的結(jié)果應(yīng)該是
{
    "userVM":[
        {
            "viewModel": userViewModel,
            "element": 
,
            "expression": "vm.username",
            "attributeName": "sf-text"
        },
        {
            "viewModel": userViewModel,
            "element": ,
            "expression": "vm.username",
            "attributeName": "sf-value"
        }
    ]
}

我的實現(xiàn)中特地定一個了一個BoundItem類來描述 {"viewModel":viewModel,"element":element,"expression":expression,"attributeName":attributeName}

//BoundItem.ts
export class BoundItem {
    public viewModel: object;
    public element: Element;
    public expression: string;
    public attributeName: string;
 
    constructor(viewModel: object, element: Element, expression: string, attributeName: string) {
        this.viewModel = viewModel;
        this.element = element;
        this.expression = expression;
        this.attributeName = attributeName;
    } 
}

拿到view_viewModel map后，SegmentFault會調(diào)用Renderer去挨個渲染每一個BoundItem。

export class Renderer{
    public render(boundItem:BoundItem) {};
}

好至此，幾個主要的類都一一登場了，接下去我們完善下SegmentFault類，讓ta和其它幾個類聯(lián)動起來

import {Scanner} from "./Scanner";
import {Watcher} from "./Watcher";
import {Renderer} from "./Renderer";
export let SegmentFault = class SegmentFault {
    private viewModelPool = {};
    private viewViewModelMap = {};
    private renderer = new Renderer();
    public init() {
        let scanner = new Scanner(this.viewModelPool);
        let watcher = new Watcher(this);
        //step 1, 暗中觀察各個viewModel
        for (let key in this.viewModelPool) {
            watcher.observe(this.viewModelPool[key],this.viewModelChangedHandler);
        }
        /step 2 3, 掃描DOM Tree并返回Map 
        this.viewViewModelMap = scanner.scanBindDOM();
        //step 4, 渲染DOM
        Object.keys(this.viewViewModelMap).forEach(alias=>{
            this.refresh(alias);
        });   
    };
    public registerViewModel(alias:string, viewModel:object) {
        viewModel["_alias"] = alias;
        window[alias] = this.viewModelPool[alias] = viewModel;
    };
    public refresh(alias:string){
        let boundItems = this.viewViewModelMap[alias];
        boundItems.forEach(boundItem => {
            this.renderer.render(boundItem);
        });
    }
    private viewModelChangedHandler(viewModel,prop) {
        this.refresh(viewModel._alias);
    }
}

好，寫到這里，骨架全部構(gòu)建完成，你有沒有興趣自己花點時間去填充血肉呢?
我希望你能做到

這里貼出其它幾個類的具體實現(xiàn)，僅供參考，你一定可以寫得比我更好。

也放出github地址，上面有完整工程
https://github.com/momoko8443...

以及在線演示地址
https://momoko8443.github.io/...

//Watcher.ts
export class Watcher {
    private sf;
    constructor(sf) {
        this.sf = sf;
    }
    public observe(viewModel, callback) {
        let host = this.sf;
        for (var key in viewModel) {
            var defaultValue = viewModel[key];
            (function (k, dv) {
                if (k !== "_alias") {
                    Object.defineProperty(viewModel, k, {
                        get: function () {
                            return dv;
                        },
                        set: function (value) {
                            dv = value;
                            console.log("do something after set a new value");
                            callback.call(host, viewModel, k);
                        }
                    });
                }
            })(key, defaultValue);
        }
    }
}

//Scanner.ts
import { BoundItem } from "./BoundItem";
export class Scanner {
    private prefix = "sf-";
    private viewModelPool;

    constructor(viewModelPool) {
        this.viewModelPool = viewModelPool;
    }
    public scanBindDOM() :object{
        let boundMap = {};
        
        let boundElements = this.getAllBoundElements(this.prefix);
        boundElements.forEach(element => {
           for (let i = 0; i < element.attributes.length; i++) {
                let attr = element.attributes[i];
                if (attr.nodeName.search(this.prefix) > -1) {
                    let attributeName = attr.nodeName;
                    let expression = element.getAttribute(attributeName);
                    for (let alias in this.viewModelPool) {
                        if (expression.search(alias + ".") != -1) {
                            let boundItem = new BoundItem(this.viewModelPool[alias], element, expression,attributeName);
                            if (!boundMap[alias]) {
                                boundMap[alias] = [boundItem];
                            } else {
                                boundMap[alias].push(boundItem);
                            }
                        }
                    }
                }
            }
        });  
        return boundMap;
    }

    private fuzzyFind(element:HTMLElement,text:string):HTMLElement {
        if (element && element.attributes) {
            for (let i = 0; i < element.attributes.length; i++) {
                let attr = element.attributes[i];
                if (attr.nodeName.search(text) > -1) {
                    return element;
                }
            }
        }
        return null;
    }
     private getAllBoundElements(prefix): Array {
        let elements = [];
        let allChildren = document.querySelectorAll("*");
        for (let i = 0; i < allChildren.length; i++) {
            let child: HTMLElement = allChildren[i] as HTMLElement;
            let matchElement = this.fuzzyFind(child, prefix);
            if (matchElement) {
                elements.push(matchElement);
            }
        }
        return elements;
    }
}

//BoundItem.ts
export class BoundItem {
    public viewModel: object;
    public element: Element;
    public expression: string;
    public attributeName: string;
    private interactiveDomConfig = {
        "INPUT":{
            "text":"input",
            "password":"input",
            "email":"input",
            "url":"input",
            "tel":"input",
            "radio":"change",
            "checkbox":"change",
            "color":"change",
            "date":"change",
            "datetime":"change",
            "datetime-local":"change",
            "month":"change",
            "number":"change",
            "range":"change",
            "search":"change",
            "time":"change",
            "week":"change",
            "button":"N/A",
            "submit":"N/A"
        },
        "SELECT":"change",
        "TEXTAREA":"change"
    }
    constructor(viewModel: object, element: Element, expression: string, attributeName: string) {
        this.viewModel = viewModel;
        this.element = element;
        this.expression = expression;
        this.attributeName = attributeName;
        this.addListener(this.element,this.expression);
    }

    private addListener(element,expression){
        let tagName = element.tagName;
        let eventName = this.interactiveDomConfig[tagName];
        if(!eventName){
            return;
        }
        if(typeof eventName === "object"){
            let type = element.getAttribute("type");
            eventName = eventName[type];
        }
        element.addEventListener(eventName, (e)=> {
            let newValue = (element as HTMLInputElement).value;
            let cmd = expression + "= "" + newValue + """;
            try{
                eval(cmd);
            }catch(e){
                console.error(e);
            }
        });
    }
}

//Renderer.ts
import {BoundItem} from "./BoundItem";
export class Renderer{
    public render(boundItem:BoundItem) {
        var value = this.getValue(boundItem.viewModel, boundItem.expression);
        var attribute = boundItem.attributeName.split("-")[1];

        if (attribute.toLowerCase() === "innertext") {
            attribute = "innerText";
        }
        boundItem.element[attribute] = value;
    };
    private getValue(viewModel, expression) {
        return (function () {
            var alias = viewModel._alias;
            var tempScope = {};
            tempScope[alias] = viewModel;
            try {
                var pattern = new RegExp("" + alias + "", "gm");
                expression = expression.replace(pattern, "tempScope." + alias);
                var result = eval(expression);
                tempScope = null;
                return result;
            } catch (e) {
                throw e;
            }
        })();
    }
}

【教學(xué)向】150行代碼教你實現(xiàn)一個低配版的MVVM庫（1）- 原理篇
【教學(xué)向】150行代碼教你實現(xiàn)一個低配版的MVVM庫（2）- 代碼篇
【教學(xué)向】再加150行代碼教你實現(xiàn)一個低配版的web component庫（1） —設(shè)計篇
【教學(xué)向】再加150行代碼教你實現(xiàn)一個低配版的web component庫（2） —原理篇