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
}
Putting everything in a loop:
HTML
<div *ngFor="let class of classes; let i = index">
<button [disabled]="currentLesson !== i + 1" class="primair">
Start lesson {{i + 1}}</button>
</div>
Typescript
currentLesson:string;
classes = [
{
name: 'Lesson1',
level: 1,
code: 1,
},{
name: 'Lesson2',
level: 1,
code: 2,
},
{
name: 'Lesson3',
level: 2,
code: 3,
}]