angular1脏值监测 模拟实现

/*
*
*/

function Scope(){
    this.$$watchers = [];
}
//valueEq为真时，基于值的检查开启。
Scope.prototype.$watch = function(watchFn, listenerFn, valueEq){
    var watcher = {
        watchFn: watchFn,
        listenerFn: listenerFn || function() {},
        valueEq: !!valueEq
    };
    this.$$watchers.push(watcher);
}

Scope.prototype.$digestOnce = function(){
    var self = this;
    var dirty;
    _.forEach(this.$$watchers,function(watch){
        var newValue = watch.watchFn(self);
        var oldValue = watch.last;
        if(newValue !== oldValue){
            watch.listenerFn(newValue, oldValue, self);
            dirty = true;
        }
        watch.last = (watch.valueEq ? _.cloneDeep(newValue) : newValue);
    });
    return dirty;
}

Scope.prototype.$digest = function(){
    var ttl = 10;
    var dirty;
    do{
        dirty = this.$$digestOnce();
        if(dirty && !(ttl--)){
            throw "10 digest iterations reached";
        }
    }while(dirty);
}

//值相等检测函数
Scope.prototype.$$areEqual = function(newValue, oldValue, valueEq){
    if(valueEq){
        return _.isEqual(newValue, oldValue);//如果是对象或数组，递归按值比较
    }else{
        return newValue === oldValue ||
            (typeof newValue === 'number' && typeof oldValue === 'number'
                && isNaN(newValue) && isNaN(oldValue));//非数字(NaN判断)
    }
}

Scope.prototype.$eval = function(expr, locals){
    return expr(this, locals);
}

Scope.prototype.$apply = function(expr){
    try{
        return this.$eval(expr);

    }finally{
        this.$digest();
    }
}

var scope = new Scope();
scope.firstName = 'Joe';
scope.counter = 0;

scope.$watch(
    function(scope){
        return scope.counter;
    },
    function(newValue, oldValue, scope){
        scope.counterIsTwo = (newValue ===2);
    }
);
scope.$watch(
    function(scope){
        return scope.firstName;
    },
    function(newValue, oldValue, scope){
        scope.counter++;
    }
);

//After the first digest the counter is 1
scope.$digest();
console.assert(scope.counter === 1);//正确

// On the next change the counter becomes two, and the other watch listener is also run because of the dirty check
scope.firstName = 'Jane';
scope.$digest();
console.assert(scope.counter === 2);//正确
console.assert(scope.counterIsTwo);//正确

http://teropa.info/blog/2013/11/03/make-your-own-angular-part-1-scopes-and-digest.html
https://github.com/spring-fe/angular1x