javascript group by, filter implementation

gistfile1.js

var list = [
    {name: "1", lastname: "foo1", age: "16"},
    {name: "2", lastname: "foo", age: "13"},
    {name: "3", lastname: "foo1", age: "11"},
    {name: "4", lastname: "foo", age: "11"},
    {name: "5", lastname: "foo1", age: "16"},
    {name: "6", lastname: "foo", age: "16"},
    {name: "7", lastname: "foo1", age: "13"},
    {name: "8", lastname: "foo1", age: "16"},
    {name: "9", lastname: "foo", age: "13"},
    {name: "0", lastname: "foo", age: "16"}
];

var result = [];

list.forEach(function(item, arr, index){
    if(item.age !== "16") {
        result.push(item);
    }
});

console.log(result);

//condition = [16,13,11]
//op = true/false
function filter(list, property, condition, op) {
     var result = [];
     list.forEach(function(item, arr, index) {
            condition.forEach(function (cond) {
                if ( (item[property] === cond) === op ) {
                    result.push(item);
                }    
            });
     });  
     
     return result; 
}

//

//[
groupBy(list, property){}

"16":[{}],
"13":[{}],
"11":[{}]
]
function groupBy(list, property){
    var result= [],
        holder = {};
    
    list.forEach(function (item, index, ar){
        if (holder[item[property]]) {
            holder[item[property]].push(item);
        } else {
            holder[item[property]] = [item];
        }
    });
 
    return holder;
} 

var list = [
    {name: "1", lastname: "foo1", age: "16"},
    {name: "2", lastname: "foo", age: "13"},
    {name: "3", lastname: "foo1", age: "11"},
    {name: "4", lastname: "foo", age: "11"},
    {name: "5", lastname: "foo1", age: "16"},
    {name: "6", lastname: "foo", age: "16"},
    {name: "7", lastname: "foo1", age: "13"},
    {name: "8", lastname: "foo1", age: "16"},
    {name: "9", lastname: "foo", age: "13"},
    {name: "0", lastname: "foo", age: "16"}
];



function groupByCounts(list, property){
    var result= [],
        holder = {};
    
    list.forEach(function (item, index, ar){
        if (holder[item[property]]) {
            holder[item[property]]++;
        } else {
            holder[item[property]] = 1;
        }
    });

    return holder;
}