How does Stack Overflow mirror what you're typing?

Question

Right now while I'm typing this there's the preview down below the editor. I would like to do something similar. How does Stack Overflow do this?

Answer 1

They use an HTML editor called WMD Markdown Editor.

Answer 2

$(function(){
    // whenever the text in the editor box changes:
    $("#editorTextArea").change(function(){
        // add the text to the preview box below
        // this certainly involves some formatting/marking up of the text
        // but this is good enough for illustrative purposes
        $("#previewBox").val(this.value);
    });
});