想通过Javascripts map,reduce,foreach,filter方法实现功能

Question

请帮我写出更好的代码。

假设我有一个如下所示的 JavaScript 数组：

var students = [
    { firstname: "stud1", lastname: "stud2", marks: "60" },
    { firstname: "stud3", lastname: "stud4", marks: "30" },
    { firstname: "stud5", lastname: "stud6", marks: "70" },
    { firstname: "stud7", lastname: "stud8", marks: "55" },
    { firstname: "stud9", lastname: "stud10", marks: "20" },
];

在页面上我想分两部分显示数据，1)得分>=40的学生2)得分<40的学生

通过使用 for 循环，我很容易地完成了这个功能，如下所示。

var data = "";var data1 = "";
for (var i = 0; i < students.length; i++ )
{
    if(students.marks >= 40){
        data += = students.firstname + " " + students.lastname; //actual data in html div tag
        ....
    }else{
            data1 += = students.firstname + " " + students.lastname;
    }
}

我想通过使用 JavaScript 方法（如 map、reduce、foreach、filter 等）实现相同的功能（想提高我的 JavaScript 知识）

不确切知道哪种方法对此类功能有用。

使用 map 方法并尝试显示数据，但每个 object/array.

末尾都有一个尾随 ,

任何人都可以 help/guide 我编写正确的代码吗？

Answer 1

这是使用 filter 和 forEach 方法，使用 callback 函数的解决方案。

在此处查看参考资料：

filter method

var students = [
    { firstname: "stud1", lastname: "stud2", marks: "60" },
    { firstname: "stud3", lastname: "stud4", marks: "30" },
    { firstname: "stud5", lastname: "stud6", marks: "70" },
    { firstname: "stud7", lastname: "stud8", marks: "55" },
    { firstname: "stud9", lastname: "stud10", marks: "20" },
];
students.filter(function(item){
    return item.marks>=40;  
}).forEach(function(item){
    div=document.getElementById('persons');
    div.innerHTML+=item.firstname+' '+item.lastname+'<br>';
});

<div id="persons"></div>

Answer 2

您可以使用单个循环并添加以 predicate 作为索引的信息。稍后加入元素以获得每个元素的刺痛。

var students = [{ firstname: "stud1", lastname: "stud2", marks: "60" }, { firstname: "stud3", lastname: "stud4", marks: "30" }, { firstname: "stud5", lastname: "stud6", marks: "70" }, { firstname: "stud7", lastname: "stud8", marks: "55" }, { firstname: "stud9", lastname: "stud10", marks: "20" }], 
    predicate = function (o) { return o.marks >= 40; },
    result = [[], []];      

students.forEach(function (a) {
    result[+predicate(a)].push(a.firstname + ' ' + a.lastname);
});
result = result.map(function (a) { return a.join(', '); });

console.log(result);

想通过Javascripts map,reduce,foreach,filter方法实现功能

Want to achieve functionality by using Javascripts map,reduce,foreach,filter methods

javascript

arrays

reduce

dictionary

filter