SxsnPC/node_modules/quill/formats/indent.js

import Parchment from 'parchment';

class IdentAttributor extends Parchment.Attributor.Class {
  add(node, value) {
    if (value === '+1' || value === '-1') {
      let indent = this.value(node) || 0;
      value = (value === '+1' ? (indent + 1) : (indent - 1));
    }
    if (value === 0) {
      this.remove(node);
      return true;
    } else {
      return super.add(node, value);
    }
  }

  canAdd(node, value) {
    return super.canAdd(node, value) || super.canAdd(node, parseInt(value));
  }

  value(node) {
    return parseInt(super.value(node)) || undefined;  // Don't return NaN
  }
}

let IndentClass = new IdentAttributor('indent', 'ql-indent', {
  scope: Parchment.Scope.BLOCK,
  whitelist: [1, 2, 3, 4, 5, 6, 7, 8]
});

export { IndentClass };