var cnvsGrad = require('canvas-gradaint');

//canvas setup
var canvas  =  document.createElement('canvas');
canvas.width = '500';
canvas.height = '300';
canvas.style.outline = "1px solid black";
document.body.appendChild(canvas);

// Get the context.
var ctx = canvas.getContext('2d');

// Set up color stop points
var cs = [
  {color:"black", position:0},
  {color:"grey",position:0.5},
  {color:"white",position:1}
];

// Draw gradient.
cnvsGrad(ctx).linear(0,0,500,0,cs);

// Similarly for radial cnvsGrad(ctx).radial(100,100,100,0,cs);