如何在Javascript中使用forEach方法或数组对象的任何数组方法？

Question

I'm learning to use modern array methods on arrays, but is there a way I can use these methods on objects of arrays? If not is it better to store the entire object into an array?

var course = {
  name: "My Javascript Tutorial",
  awesome: true,
  teachers: ["Brandon", "Shane", "Mike"],
  students: [
    {
      name: "Cliff",
      computer: {
        OS: "macOS",
        type: "iMac"
      }
    },
    {
      name: "Arthur",
      computer: {
        OS: "macOS",
        type: "Macbook Pro"
      }
    },
    {
      name: "Donald",
      computer: {
        OS: "macOS",
        type: "Windows PC"
      }
    }
  ]
};


course.forEach(function(item){
    console.log(course.students[item].name + 'uses a ' + course.students[item].computer.type);
})

This is the Error I'm getting.

TypeError: Cannot read property 'students' of undefined

Answer 1

The array you want to iterate over is course.students , so reference course.students and call forEach on it.

The first argument to forEach will be the item being iterated over (an element of the array). Because your elements are objects, reference their name and computer properties to log them properly:

 var course = { name: "My Javascript Tutorial", awesome: true, teachers: ["Brandon", "Shane", "Mike"], students: [ { name: "Cliff", computer: { OS: "macOS", type: "iMac" } }, { name: "Arthur", computer: { OS: "macOS", type: "Macbook Pro" } }, { name: "Donald", computer: { OS: "macOS", type: "Windows PC" } } ] }; course.students.forEach(function(item){ console.log(item.name + 'uses a ' + item.computer.type); }) 

Answer 2

forEach() function call is supported only for the arrays, not for the objects.

In your case, if you want to traverse the array students, then you have to first get the reference to the students array from the course object.

This is how you can proceed:

    course.students.forEach(function(item){
console.log(item.name + 'uses a ' + item.computer.type); })

Answer 3

If you want to loop through your students array inside the object then you have to use indexes in the array, hence add an i variable in the foreEach

course.students.forEach(function(item, i) {
    console.log(course.students[i].name + 'uses a ' + course.students[i].computer.type);
})

Or just use the object/item and display the properties of that object in every iteration

course.students.forEach(function (item) {
  console.log(item.name + 'uses a ' + item.computer.type);
})

Answer 4

The problem is, that you are trying to use the forEach loop on a object, which is not supported. Next you have the problem that you are trying to call the student name inside of a function, where it can't find the value course directly.

What you can do is following:

course.students.forEach(function(student) {
    console.log(student.name); 
});