let people = [

    {id: 1, name: "a", age: 12},

    {id: 2, name: "b", age: 13},

    {id: 3, name: "c", age: 14},

    {id: 4, name: "d", age: 15},

    {id: 5, name: "e", age: 16}

];

const kids = [];

people.forEach(person => {

    if (person.age < 15) {

        kids.push({

            id: person.id,

            name: person.name

        })

    }

});

console.log(kids);

//map & filter都是数组的方法！

//返回项参与的表达式值

const numbers = [1, 2, 3, 4, 5];

const doubled = numbers.map(number => number * 2); //[2,4,6,8,10]

console.log(doubled);

//返回满足条件的项

const even = numbers.filter(number => number % 2 === 0); //[2,4]

console.log(even);

//把用forEach示例重写

const kids2 = people

    .filter(person => person.age < 15)

    .map(person => ({

        id: person.id,

        name: person.name

    }));

console.log(kids2);

/*

结论：从上面的示例可知，filter相当于C#的where过滤条件，map相当于C#的select投影

*/