Objects

• Objects can be created as well

  • let point = {
       x: 0,
       y: 0
    }; 

  • Access to member data is through the . operator.
    • So this is fine

    • ctx.moveTo(points[0].x+cx, points[0].y+cy);
      for (let i=1; i < points.length; i++) {
            ctx.lineTo(points[i].x+cx, points[i].y+cy);
      }
      ctx.stroke(); 

  • Unfortunately, we have the shallow copy problem so this does not work

    • let point = {
          x: 0,
          y: 0
      };
      
      for(i=0;i<=size;i++) {
            point.x= r * Math.cos(theta);
            point.y = r * Math.sin(theta);
            points.push(point);
            theta+= angle;
      } 

    • This will push the same object multiple times.
    • And each time, modify all instances of the object.
    • We are pushing a pointer here.
  • Here is my solution

    • let xCord,yCord;
      
      for(i=0;i<=size;i++) {
            xCord = r * Math.cos(theta);
            yCord = r * Math.sin(theta);
            points.push({x:xCord, y:yCord});
            theta+= angle;
      } 

• Note: comparison of objects is shallow as well.
• Note: const is only the pointer, not the thing the pointer is pointing at.
  • An example from the book.

  • const score = {visitors: 0, home: 0};
    // This is okay
    score.visitors = 1;
    // This isn't allowed
    score = {visitors: 1, home: 1};
            

• eight.js