Script Error (js)

I have 1 error in this script.

 function Update() {
     var mesh : Mesh= MeshRenderer.mesh;
     var colors : Color[] = mesh.colors;
     
     for (var i=0;i<colors.Length;i++) 
     {
       var _color : Color = colors[i];
       _color.a = 1.0;  
       colors[i] = _color;
     }
     mesh.colors = colors;  
     }

(2,31): BCE0019: 'mesh' is not a member of 'UnityEngine.MeshRenderer'.

How to fix???