Open or disable buttons with an angular shape

I'm making an web-app in angular 4 and there is a question i came up with. It's the following:

I use a property called currentLesson. This property has a variable number from 1 to 6. In my component I have an list of 6 lessons where each lesson has it's own button to start this lesson.

In this list it should only be possible to click the button when the current lesson value consists of the number of lessons

Button of lesson 1 is active when : currentLesson = 1

Button of lesson 2 is active when : currentLesson = 2

Etc. etc.

So if currentlesson = 2, the buttons of lesson 1, 3, 4, 5 and 6 should be disabled.

I have the following set-up but it doesn't seem to work. In my component i have:

export class ClassComponent implements OnInit {
  classes = [
{
  name: 'string',
  level: 'string',
  code: 'number',
  currentLesson: '1'
}]



checkCurrentLesson1 = function(classes) {
if (classes.currentLesson = 1) {
 return true;
}
else {
 return false;
}
};

checkCurrentLesson2 = function(classes) {
if (classes.currentLesson = 2) {
 return true;
}
else {
 return false;
}
};

My html file is the same

 <ul class="table lessonOverview">
    <li>
      <p>Lesson 1</p>
      <button [routerLink]="['/lesson1']"
         [disabled]="!checkCurrentLesson1" class="primair">
           Start lesson</button>
    </li>
    <li>
      <p>Lesson 2</p>
      <button [routerLink]="['/lesson2']"
         [disabled]="!checkCurrentLesson2" class="primair">
           Start lesson</button>
    </li>
 </ul>

(I only printed two of the six lessons, but they are all the same)

How do i get a solution for my problem?

Thanks in advance,

Maarten

Set a property for the current lesson: currentLesson. It will hold, obviously, the 'number' of the choosen lesson. On each button click, set the currentLesson value to 'number'/ order of the button, i.e. for the first button, it will be '1', for the second '2' and so on. Each button now can be disabled with [disabled] attribute, if it the currentLesson is not the same as it's order.

HTML

  <button  (click)="currentLesson = '1'"
         [disabled]="currentLesson !== '1'" class="primair">
           Start lesson</button>
  <button (click)="currentLesson = '2'"
         [disabled]="currentLesson !== '2'" class="primair">
           Start lesson</button>
 .....//so on

Typescript

currentLesson:string;

  classes = [
{
  name: 'string',
  level: 'string',
  code: 'number',
  currentLesson: '1'
}]

constructor(){
  this.currentLesson=this.classes[0].currentLesson
}

DEMO

Putting everything in a loop

HTML

<div *ngFor="let class of classes; let i = index">
   <button [disabled]="currentLesson !== i + 1" class="primair">
           Start lesson </button>
</div>

Typescript

currentLesson:string;

classes = [
{
  name: 'Lesson1',
  level: 1,
  code: 1,
},{
  name: 'Lesson2',
  level: 1,
  code: 2,
},
{
  name: 'Lesson3',
  level: 2,
  code: 3,
}]

DEMO