CodeMirror 4 use spaces instead of tabs

cm_config.coffee

cm_config = {}
cm_config['extraKeys'] = {
  "Tab": checkToUseSpacesInsteadofTabs
}
CodeMirror($(".code")[0], cm_config)

spaces-or-tabs.coffee

checkToUseSpacesInsteadofTabs = (cm) ->
    if(cm.getOption("indentWithTabs"))
        return CodeMirror.Pass
    indentUnit = cm.getOption("indentUnit")
    getYoSpaceCount = (head) ->
        # Use preceding to determine what room is taken by tabs
        preceding = cm.getRange {line:head.line, ch:0}, head
        tabCount = 0
        tabreg = /\t/g
        while(tabreg.exec preceding)
            tabCount++
        return indentUnit - (head.ch + tabCount*(indentUnit - 1)) % indentUnit
    makeYoSpaces = (spaceCount) ->
        spaces = ""
        for [1..spaceCount]
            spaces += " "
        return spaces
    putYoSpacesHere = (range) ->
        {anchor, head} = range
        if anchor.line isnt head.line or anchor.ch isnt head.ch
            for line in [anchor.line..head.line]
                curLine = cm.getLine(line)
                curPos = {line, ch:0}
                cm.replaceRange makeYoSpaces(indentUnit), curPos, curPos
            #anchor.ch += indentUnit
            #head.ch += indentUnit
        else
            cm.replaceRange makeYoSpaces(getYoSpaceCount(head)), anchor, head
    cm.doc.sel.ranges.forEach putYoSpacesHere