Get a specific item length in array object [nodejs]

Question

I want to get the length of an array that match the value specified by the condition.

var school = {
 student : {
 name: Json,
 class: 0,
 type: male,
 average: B+
 },
 student : {
 name: Afrado,
 class: 0,
 type: male,
 average: C+
 },
 student : {
 name: Emily,
 class: 1,
 type: female,
 average: A+
 }
};

I'd like to know the lengh of class "0" but I don't know how to resolve this case?
In this case I can get the length of "2" for my results.

Have a nice day~ :)

Answer 1

Your array is not structured properly, what you need to do is to filter and get the length of the filtered items.

var school = [
 {
 name: "Json",
 class: 0,
 type: "male",
 average: "B+"
 },
 {
 name: "Afrado",
 class: 0,
 type: "male",
 average: "C+"
 },
 {
 name: "Emily",
 class: "1",
 type: "female",
 average: "A+"
 }
];
console.log(school.filter(student => student.class === 0).length);

Answer 2

You can use the reduce function to avoid creating a temporary array with filter.

console.log(school.reduce((count, student) => student.class === 0 ? ++count : count, 0));

Answer 3

you can also use this way:

var school = [
 {
 name: "Json",
 class: 0,
 type: "male",
 average: "B+"
 },
 {
 name: "Afrado",
 class: 0,
 type: "male",
 average: "C+"
 },
 {
 name: "Emily",
 class: "1",
 type: "female",
 average: "A+"
 }
];
function search(className, myArray){
 var countClass = 0;
 for (var i=0; i < myArray.length; i++) {
 if (myArray[i].class === className) {
 countClass++;
 }
 }
 return countClass;
}
function searchForeach(className, myArray){
 var countClass = 0;
 myArray.forEach((item) => {
 if (item.class === className) {
 countClass++;
 }
 });
 return countClass;
}
function searchFind(className, myArray){
 var countClass = 0;
 myArray.find((item, index) => {
 if (item.class === className) {
 countClass++;
 }
 });
 return countClass;
}
console.log(search(0, school));
console.log(searchForeach("1", school));
console.log(searchFind(0, school));

second way use find: