A CodeMirror command to delete 4-space indent or charactor before.

cmindent.js

/**
 * > if foo:
 * >     |   <= The cursor is here and hit delCharOrIndent command, it willbe
 * > | <= here
 * 
 * This command will delete at most 4 spaces before, if text before charactor is all spaces.
 * If not on the case, this command will delete charactor as usual.
 */

(function(mod) {
  if (typeof exports == "object" && typeof module == "object") // CommonJS
    mod(require("codemirror/lib/codemirror"));
  else if (typeof define == "function" && define.amd) // AMD
    define(["codemirror/lib/codemirror"], mod);
  else // Plain browser env
    mod(CodeMirror);
})(function(CodeMirror) {
  "use strict";
  var SPACES_REGEXP = /^( +$)/;
  
  CodeMirror.commands.delCharOrIndent = function(cm) {
    // Dedening 4-space indents or deleting char before.

    // Getting from the top of line to the cursor
    var c = cm.getCursor();
    var lineText = cm.getRange({line: c.line, ch: 0}, {line: c.line, ch: c.ch});

    // Detecting whether the lineText contains only spaces.
    var m = SPACES_REGEXP.exec(lineText);
    if (m) {
      // If only spaces, deleting at most 4 spaces.
      var numDelete = m[1].length < 4 ? m[1].length : 4;
      return cm.replaceRange('', {line: c.line, ch: 0}, {line: c.line, ch: numDelete});
    } else {
      return CodeMirror.commands.delCharBefore(cm);
    }
  }
});