test2.html

<canvas id="c"></canvas>
<script id="vertex-shader-2d" type="notjs">
 
  // an attribute will receive data from a buffer
  attribute vec4 a_position;
 
  // all shaders have a main function
  void main() {
 
    // gl_Position is a special variable a vertex shader
    // is responsible for setting
    gl_Position = a_position;
  }
 
</script>
 
<script id="fragment-shader-2d" type="notjs">
 
  // fragment shaders don't have a default precision so we need
  // to pick one. mediump is a good default
  precision mediump float;
 
  void main() {
    // gl_FragColor is a special variable a fragment shader
    // is responsible for setting
    gl_FragColor = vec4(1, 0, 0.5, 1); 
  }
 
</script>
<script>
var canvas = document.querySelector("#c");
var gl = canvas.getContext("webgl");
function createShader(gl, type, source) {
  var shader = gl.createShader(type);
  gl.shaderSource(shader, source);
  gl.compileShader(shader);
  var success = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
  if (success) {
    return shader;
  }
 
  console.log(gl.getShaderInfoLog(shader));
  gl.deleteShader(shader);
}

function createProgram(gl, vertexShader, fragmentShader) {
  var program = gl.createProgram();
  gl.attachShader(program, vertexShader);
  gl.attachShader(program, fragmentShader);
  gl.linkProgram(program);
  var success = gl.getProgramParameter(program, gl.LINK_STATUS);
  if (success) {
    return program;
  }
 
  console.log(gl.getProgramInfoLog(program));
  gl.deleteProgram(program);
}

var vertexShaderSource = document.querySelector("#vertex-shader-2d").text;
var fragmentShaderSource = document.querySelector("#fragment-shader-2d").text;
 
var vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
var fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);

var program = createProgram(gl, vertexShader, fragmentShader);
var positionAttributeLocation = gl.getAttribLocation(program, "a_position"); // do during initialisation, not render loop :3c
var positionBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
var positions = [
  0, 0,
  0, 0.5,
  0.7, 0,
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);
//all this here is initialisation (runs once when we load the page)
//now  is rendering (executed everytime we want to render / draw)
gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
gl.clearColor(0, 0, 0, 0);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.useProgram(program);
gl.enableVertexAttribArray(positionAttributeLocation);//turn attribute on
//how to pull data out
// Bind the position buffer.
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
 

var size = 2;          
var type = gl.FLOAT;   
var normalize = false; 
var stride = 0;        
var offset = 0;        
gl.vertexAttribPointer(
    positionAttributeLocation, size, type, normalize, stride, offset)

var primitiveType = gl.TRIANGLES;
var offset = 0;
var count = 3;
gl.drawArrays(primitiveType, offset, count);
</script>