checkfb.js

var gl = document.createElement("canvas").getContext("webgl");
var tex = gl.createTexture();
gl.bindTexture(gl.TEXTURE_2D, tex);
var fb = gl.createFramebuffer();
gl.bindFramebuffer(gl.FRAMEBUFFER, fb);
gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, tex, 0);
[
  "ALPHA",
  "LUMINANCE",
  "LUMINANCE_ALPHA",
  "RGB",
  "RGBA",
].forEach(function(format) {
  gl.texImage2D(gl.TEXTURE_2D, 0, gl[format], 1, 1, 0, gl[format], gl.UNSIGNED_BYTE, null);
  var canRender = gl.checkFramebufferStatus(gl.FRAMEBUFFER) == gl.FRAMEBUFFER_COMPLETE;
  console.log(format, canRender ? "can render" : "can not render");
});