JavaScript实现依赖注入

var cache = {};

// 通过解析Function.prototype.toString()取得参数名

function getParamNames(func) {

    // 正则表达式出自http://krasimirtsonev.com/blog/article/Dependency-injection-in-JavaScript

    var paramNames = func.toString().match(/^functions*[^(]*(s*([^)]*))/m)[1];

    paramNames = paramNames.replace(/ /g, '');

    paramNames = paramNames.split(',');

    return paramNames;

}

var injector = {

    // 将func作用域中的this关键字绑定到bind对象上，bind对象可以为空

    resolve: function (func, bind) {

        // 取得参数名

        var paramNames = getParamNames(func);

        var params = [];

        for (var i = 0; i < paramNames.length; i++) {

            // 通过参数名在cache中取出相应的依赖

            params.push(cache[paramNames[i]]);

        }

        // 注入依赖并执行函数

        func.apply(bind, params);

    }

};

  

function Notebook() {}

Notebook.prototype.printName = function () {

    console.log('this is a notebook');

};

  

function Pencil() {}

Pencil.prototype.printName = function () {

    console.log('this is a pencil');

};

  

function Student() {}

Student.prototype.write = function (notebook, pencil) {

    if (!notebook || !pencil) {

        throw new Error('Dependencies not provided!');

    }

    console.log('writing...');

};

// 提供notebook依赖

cache['notebook'] = new Notebook();

// 提供pencil依赖

cache['pencil'] = new Pencil();

var student = new Student();

injector.resolve(student.write, student); // writing...