How do you convert a color image to black/white using Javascript?

Question

How do you convert a color image to black/white using only Javascript?

AND, also make it cross compatible in most browsers because I hear Internet E

Answer 1

Modern browsers can now do this in CSS – on any HTML element, not just images. Combined with IE's old filter CSS, you can get pretty good compatibility:

image.grayscale {
  /* IE */
  filter: progid:DXImageTransform.Microsoft.BasicImage(grayscale=1);

  /* Chrome, Safari */
  -webkit-filter: grayscale(1);

  /* Firefox */
  filter: grayscale(1);
}

OP specifies "only JavaScript" but also mentions that IE's filter would be acceptable if it were more widely supported, which it now (effectively) is, so I believe this is the best solution in 2015. If you really must have JavaScript:

element.style.filter = 'grayscale(1)';

Sources:

• Browser support
• Spec
• Tutorial