way to change a color to transparency on a png

hello I need to create in javascript something to change a color to transparent, on PNG I’d like to create a form that, when I post a picture, everything white should be transformed to transparent and generated as a new PNG, however this white is coming from a picture so it won’t be exactly white but contrast are good since this will pictures of text written on a white page maybe some king of green screen algo any ideas on how to do that ?