function getProgram(gl, vs, fs) {
  const vertexShader = getShader(gl, vs, 'vertex');
  const fragmentShader = getShader(gl, fs, 'fragment');
  if (!fragmentShader) {
    return null;
  }

  const shaderProgram = gl.createProgram();
  gl.attachShader(shaderProgram, vertexShader);
  gl.attachShader(shaderProgram, fragmentShader);
  gl.linkProgram(shaderProgram);

  const result = gl.getProgramParameter(shaderProgram, gl.LINK_STATUS);
  if (!result) {
    alert('Could not initialise arview shaders');
  }

  return shaderProgram;
}
Creates a shader program from vertex and fragment shader sources

@param {WebGLRenderingContext} gl
@param {string} vs
@param {string} fs
@return {!WebGLProgram}