WebGLRenderingContext.linkProgram()

var program = gl.createProgram();

// Attach pre-existing shaders
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);

gl.linkProgram(program);

if ( !gl.getProgramParameter( program, gl.LINK_STATUS) ) {
  var info = gl.getProgramInfoLog(program);
  throw new Error('Could not compile WebGL program. \n\n' + info);
}