Resizing on-screen WebGL canvas in iOS Safari causes memory leak

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<canvas>Your browser does not support HTML5 canvas.</canvas>

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* { margin:0; padding:0; }
html, body { width: 100%; height: 100%; }
canvas { display: block; }

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var _canvas;
var _gl;
var _buffer;
var _shaderProgram;
var _coordinatesVar;
var _widths = [768, 1024];
var _heights = [1024, 768];
var _dimIndex = 0;
var _resizeStartTime = undefined;
function _setupScene() {
  _canvas = document.getElementsByTagName("canvas")[0];
  _gl = _canvas.getContext("webgl") || _canvas.getContext("experimental-webgl");
  if (!_gl)
    throw new Error("Cannot create WebGL context!");
  var vertices = [
    -0.5, 0.5,
    -0.5, -0.5,
    0.5, -0.5,
    0.5, -0.5,
    -0.5, 0.5,
    0.5, 0.5,
  ];
  _buffer = _gl.createBuffer();
  _gl.bindBuffer(_gl.ARRAY_BUFFER, _buffer);
  _gl.bufferData(_gl.ARRAY_BUFFER, new Float32Array(vertices), _gl.STATIC_DRAW);
  
  var vertCode =
    'attribute vec2 coordinates;' +
    'void main(void) {' +
    '  gl_Position = vec4(coordinates, 0.0, 1.0);' +
    '}';
  var vertShader = _gl.createShader(_gl.VERTEX_SHADER);
  _gl.shaderSource(vertShader, vertCode);
  _gl.compileShader(vertShader);
  if (!_gl.getShaderParameter(vertShader, _gl.COMPILE_STATUS))
    throw new Error(_gl.getShaderInfoLog(vertShader));
  var fragCode =
    'void main(void) {' +
    '   gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);' +
    '}';
  var fragShader = _gl.createShader(_gl.FRAGMENT_SHADER);
  _gl.shaderSource(fragShader, fragCode);
  _gl.compileShader(fragShader);
  if (!_gl.getShaderParameter(fragShader, _gl.COMPILE_STATUS))
    throw new Error(_gl.getShaderInfoLog(fragShader));
  _shaderProgram = _gl.createProgram();
  _gl.attachShader(_shaderProgram, vertShader);
  _gl.attachShader(_shaderProgram, fragShader);
  _gl.linkProgram(_shaderProgram);
  if (!_gl.getProgramParameter(_shaderProgram, _gl.LINK_STATUS))
    throw new Error(_gl.getProgramInfoLog(_shaderProgram));
  _gl.useProgram(_shaderProgram);
  _coordinatesVar = _gl.getAttribLocation(_shaderProgram, "coordinates");
  _gl.enableVertexAttribArray(_coordinatesVar);
  _gl.bindBuffer(_gl.ARRAY_BUFFER, _buffer);
  _gl.vertexAttribPointer(_coordinatesVar, 2, _gl.FLOAT, false, 0, 0);
  
  /* initial auto-resize */
	_canvas.width = _widths[_dimIndex];
	_canvas.height = _heights[_dimIndex];
  _dimIndex = _dimIndex > 0 ? 0 : 1;
}
function _drawScene() {
  _gl.drawArrays(_gl.TRIANGLES, 0, 6);
}
function _render(timestamp) {
	/* The following makes the canvas resizing based on browser window (fullscreen):
    _canvas.width = window.innerWidth;
    _canvas.height = window.innerHeight;
    */
  
  /* The following automatically changes the canvas dimensions back and forth between two dimensions every second: */
	if (undefined === _resizeStartTime)
  	_resizeStartTime = timestamp;
  const elapsed = timestamp - _resizeStartTime;
  if (elapsed > 1000) {
	  _canvas.width = _widths[_dimIndex];
    _canvas.height = _heights[_dimIndex];
    _dimIndex = _dimIndex > 0 ? 0 : 1;
    _resizeStartTime = undefined;
  }
  _gl.viewport(0, 0, _canvas.width, _canvas.height);
  _gl.clearColor(0.8, 0.8, 0.8, 1.0);
  _gl.clear(_gl.COLOR_BUFFER_BIT);
  
  _drawScene();
  
	window.requestAnimationFrame(_render);
}
window.addEventListener("load", function() {
	_setupScene();
	window.requestAnimationFrame(_render);
}, false);