angularjs 源码解析之injector

简介

injector是用来做参数自动注入的，例如

function fn ($http, $scope, aservice) {
}

ng在运行时会把$http, $scope, aservice 自动作为参数传入进行执行。

其实很容易想明白，injector做了两件事

1. 缓存那些service，以后作为参数注入
2. 分析参数列表，找到需要的参数注入
   

下面源码分析如何实现上面两件事情。

结构

createinjector -> createinternalinjector  return: instanceinjector


所以 createinjector() 返回的是 instanceinjector，结构如下：

{
 invoke: invoke,
 instantiate: instantiate,
 get: getservice,
 annotate: annotate,
 has: function(name) {
  return providercache.hasownproperty(name + providersuffix) || cache.hasownproperty(name);
 }
}

源码分析

1. createinjector

function createinjector(modulestoload, strictdi) {
 strictdi = (strictdi === true);
 var instantiating = {},
   providersuffix = 'provider',
   path = [],
   loadedmodules = new hashmap([], true),
   // 预先配置$provide,供loadmodules中调用注册service等
   providercache = {
    $provide: {
      provider: supportobject(provider),
      factory: supportobject(factory),
      service: supportobject(service),
      value: supportobject(value),
      constant: supportobject(constant),
      decorator: decorator
     }
   },

   // providerinjector, instanceinjector 两个注入器
   // instanceinjector对外提供service等注入，providerinjector对内提供provider获取
   providerinjector = (providercache.$injector =
     createinternalinjector(providercache, function() {
      throw $injectorminerr('unpr', "unknown provider: {0}", path.join(' <- '));
     }, strictdi)),
   instancecache = {},
   instanceinjector = (instancecache.$injector =
     createinternalinjector(instancecache, function(servicename) {
      var provider = providerinjector.get(servicename + providersuffix);
      return instanceinjector.invoke(provider.$get, provider, undefined, servicename);
     }, strictdi));

 // 加载模块
 foreach(loadmodules(modulestoload), function(fn) { instanceinjector.invoke(fn || noop); });

 return instanceinjector;
}

2. $provide

$provide: {
  provider: supportobject(provider),
  factory: supportobject(factory),
  service: supportobject(service),
  value: supportobject(value),
  constant: supportobject(constant),
  decorator: decorator
}

2.1 supportobject

用于包装方法，包装前的方法接受两个参数 (key, value)，经过包装后的方法能支持传入object参数，即多个 key -> value。

function supportobject(delegate) {
 return function(key, value) {
  if (isobject(key)) {
   foreach(key, reverseparams(delegate));
  } else {
   return delegate(key, value);
  }
 };
}

2.2 provider

回顾下provider、service 和 factory的使用方式

app.factory('servicename', function(){
 return {
  getname: function(){},
  setname: function(){}
 }
});

app.service('servicename', function(){
 this.getname = function() {}

 this.setname = function() {}
});

app.provider('servicename', function($httpprovider){
 // 注入$httpprovider
 this.$get = function() {
  return {
   getname: function(){},
   setname: function(){}
  };
 }
});

app.provider('servicename', {
  $get: function () {}
});
function provider(name, provider_) {
 assertnothasownproperty(name, 'service');
 // 当provider_是fn或者array时可以将其他provider注入到参数
 // 因为providerinjector.instantiate(provider_)时可以传入依赖的其他provider
 // 这也是provider与service,factory方法不一样的地方
 if (isfunction(provider_) || isarray(provider_)) {
  provider_ = providerinjector.instantiate(provider_);
 }
 if (!provider_.$get) {
  throw $injectorminerr('pget', "provider '{0}' must define $get factory method.", name);
 }
 return providercache[name + providersuffix] = provider_;
}

function factory(name, factoryfn) { return provider(name, { $get: factoryfn }); }

function service(name, constructor) {
 return factory(name, ['$injector', function($injector) {
  return $injector.instantiate(constructor);
 }]);
}

function value(name, val) { return factory(name, valuefn(val)); }

最终汇总到provider的实现，将provider缓存到providercache，供调用

跟其他不一样的就是constant的实现，分别保存到providercache和instancecache中，这样在定义provider还是在定义service是都能注入。

function constant(name, value) {
 assertnothasownproperty(name, 'constant');
 providercache[name] = value;
 instancecache[name] = value;
}

2.3 回顾 loadmodules

function runinvokequeue(queue) {
 var i, ii;
 for(i = 0, ii = queue.length; i < ii; i++) {
  var invokeargs = queue[i],
    provider = providerinjector.get(invokeargs[0]);
  // 存入queue的如格式[$provide, factory, arguments]
  // 经过替换，$provide.factory.apply($provide, arguments);
  // 就是调用$provid的factory，service等
  provider[invokeargs[1]].apply(provider, invokeargs[2]);
 }
}

2.4 decorator

示例:

module.config(function($provide) {
 $provide.decorator('mail', function($delegate) {
  $delegate.addcc = function(cc) {
   this.cc.push(cc);
  };
  return $delegate;
 });
})

使用示例看出，传入的参数$delegate是原先的service实例，需要在该实例上添加方法都可以，即所谓的装饰器

源码:

function decorator(servicename, decorfn) {
 var origprovider = providerinjector.get(servicename + providersuffix),
   orig$get = origprovider.$get;

 origprovider.$get = function() {
  // 通过上面获取的provider生成需要的service实例，再以$delegate注入到参数列表
  var originstance = instanceinjector.invoke(orig$get, origprovider);
  return instanceinjector.invoke(decorfn, null, {$delegate: originstance});
 };
}

3. createinternalinjector

3.1 整体结构

// 从cache中获取，没有的话调用factory进行创建,具体看getservice解析

function createinternalinjector(cache, factory) {

 function getservice(servicename) {
 }

 function invoke(fn, self, locals, servicename){
 }

 function instantiate(type, locals, servicename) {
 }

 return {
  // 执行fn，具有参数注入功能
  invoke: invoke,
  // 实例化fn, 可以参数注入
  instantiate: instantiate,
  // 获取provider或者service
  get: getservice,
  // 获取方法的参数列表，供注入使用
  annotate: annotate,
  // 确认是否含有provider或service
  has: function(name) {
   return providercache.hasownproperty(name + providersuffix) || cache.hasownproperty(name);
  }
 };
}

3.2 annotate

获取fn的参数列表

// type1
function fn (a, b, c) -> ['a', 'b', 'c']

// type2
['a', 'b', fn] -> ['a', 'b']

// type3
function fn () {}
fn.$inject = ['a', 'c']
-> ['a', 'c']

源码:

function annotate(fn, strictdi, name) {
 var $inject,
   fntext,
   argdecl,
   last;

 if (typeof fn === 'function') {
  if (!($inject = fn.$inject)) {
   $inject = [];
   if (fn.length) {
    // 严格模式下或抛错
    if (strictdi) {
     if (!isstring(name) || !name) {
      name = fn.name || anonfn(fn);
     }
     throw $injectorminerr('strictdi',
      '{0} is not using explicit annotation and cannot be invoked in strict mode', name);
    }
    // 将注释去掉
    fntext = fn.tostring().replace(strip_comments, '');
    // 将参数全部选出fn(a,b,c,d) -> 'a,b,c,d'
    argdecl = fntext.match(fn_args);
    // 分割成array
    foreach(argdecl[1].split(fn_arg_split), function(arg){
     arg.replace(fn_arg, function(all, underscore, name){
      $inject.push(name);
     });
    });
   }
   fn.$inject = $inject;
  }
 } else if (isarray(fn)) {
  last = fn.length - 1;
  assertargfn(fn[last], 'fn');
  $inject = fn.slice(0, last);
 } else {
  assertargfn(fn, 'fn', true);
 }
 return $inject;
}

3.3 getservice

// 当cache中没有该service时，进入else, 先cache[servicename] = instantiating 做一个标记
// 因为接下来调用factory(servicename)，其实是一个递归调用
// function(servicename) {
//  var provider = providerinjector.get(servicename + providersuffix);
//  return instanceinjector.invoke(provider.$get, provider, undefined, servicename);
// }
// instanceinjector.invoke(provider.$get 时会将需要注入的参数get出来然后注入
// 因此做上标记后就可以判断是否有循环依赖
function getservice(servicename) {
 if (cache.hasownproperty(servicename)) {
  if (cache[servicename] === instantiating) {
   throw $injectorminerr('cdep', 'circular dependency found: {0}',
        servicename + ' <- ' + path.join(' <- '));
  }
  return cache[servicename];
 } else {
  try {
   path.unshift(servicename);
   cache[servicename] = instantiating;
   return cache[servicename] = factory(servicename);
  } catch (err) {
   if (cache[servicename] === instantiating) {
    delete cache[servicename];
   }
   throw err;
  } finally {
   path.shift();
  }
 }
}

3.4 invoke

function invoke(fn, self, locals, servicename){
 if (typeof locals === 'string') {
  servicename = locals;
  locals = null;
 }

 var args = [],
   // 获取参数列表
   $inject = annotate(fn, strictdi, servicename),
   length, i,
   key;

 for(i = 0, length = $inject.length; i < length; i++) {
  key = $inject[i];
  if (typeof key !== 'string') {
   throw $injectorminerr('itkn',
       'incorrect injection token! expected service name as string, got {0}', key);
  }
  // locals优先
  args.push(
   locals && locals.hasownproperty(key)
   ? locals[key]
   : getservice(key)
  );
 }
 if (isarray(fn)) {
  fn = fn[length];
 }

 return fn.apply(self, args);
}

3.5 instantiate

function instantiate(type, locals, servicename) {
 var constructor = function() {},
   instance, returnedvalue;
 
 // 当type为array时，获取最后的参数如：['$window', function($win){}]
 constructor.prototype = (isarray(type) ? type[type.length - 1] : type).prototype;
 instance = new constructor();
 // 调用invoke执行type方法
 returnedvalue = invoke(type, instance, locals, servicename);

 return isobject(returnedvalue) || isfunction(returnedvalue) ? returnedvalue : instance;
}

instantiate 的作用是用来实例化type的，在实例化的过程中可以自动传入参数到构造函数。