AEM6 | RTE validator plugin

You can use the belowJS for sample validator plugin for Rich text editor-

CUI.rte.plugins.ValidatorPlugin = new Class({

    toString: "ValidatorPlugin",

    extend: CUI.rte.plugins.Plugin,

    /**
     * RTE plugin for maximun length check. If maxlength is set to 0 the validation will not happen. Set a number 
     * greater than 0 for maxlength property.
     */

    /**
     * @private
     */
    alertShown: false,
    errorEl: null,

    /**
     * @private
     */
    _init: function(editorKernel) {
        this.inherited(arguments);
        editorKernel.addPluginListener("beforekeydown", this.handleKeyDown, this, this,
            false);
        editorKernel.addPluginListener("keyup", this.handleKeyUp, this, this,
            false);
        editorKernel.addPluginListener("paste", this.handlePaste, this, this.editContext,
            false);
    },
    handlePaste: function(e, ctx) {
        var k = e.nativeEvent;
        var newtext, existingText, isIE;
        var clp = (k.originalEvent || k).clipboardData;
        var ek = this.editorKernel;
        existingText = $(e.editContext.root).context.textContent;
        if (clp === undefined || clp === null) {
            newtext = window.clipboardData.getData('Text');
            isIE = true;
        } else {
            newtext = clp.getData('text/plain');
            isIE = false;
        }

        var fulltext = existingText + newtext;
        //console.log("hi");
        //console.log("Existing: " + existingText);
        console.log("value: " + fulltext);
        var len = fulltext.length;
        if (len > this.config.maxlength && this.config.maxlength != 0) {

            this.showError(ek, "Maximum character limit: '" + this.config.maxlength + "' reached!");
            $(e.editContext.root).context.textContent = fulltext.substr(0, this.config.maxlength);
            k.preventDefault();
        }
    },

    /**
     * Handles key strokes.
     * @param {Object} e The plugin event
     * @private
     */
    handleKeyDown: function(e, k) {
        //Don't handle delete, backspace and arrow clicks
        if (e.isBackSpace() || e.isDelete() || e.isShift() || e.ctrlKeyPressed ||
            (e.charCode > 32 && e.charCode < 41)) {
            return;
        }
        var context = e.editContext;
        var dpr = CUI.rte.DomProcessor;
        var sel = CUI.rte.Selection;
        var com = CUI.rte.Common;
        var lut = CUI.rte.ListUtils;
        var ek = this.editorKernel;
        /* if(e.charCode==13)
         {
             debugger;

         }*/
        if (!this.isValidMaxLength(e, context)) {
            this.showError(ek, "Maximum character limit: '" + this.config.maxlength + "' reached!");
            e.preventDefault();
            return;
        }
    },
    showError: function(ek, message) {
        if (!this.alertShown) {
            ek.getDialogManager().alert(
                CUI.rte.Utils.i18n("Error"),
                CUI.rte.Utils.i18n(message),
                CUI.rte.Utils.scope(this.focus, this));
            this.alertShown = true;
        } else {}

    },

    /**
     * Handles post-processing required for all browsers. The method is called whenever a
     * key has been pressed.
     * @param {Object} e The plugin event
     * @private
     */
    handleKeyUp: function(e) {},
    isValidMaxLength: function(e, context) {
        if (this.config.maxlength == 0) {
            return true;
        }

        var length = context.root.textContent.length;
        var $contentEditable = $('#ContentFrame').contents().find('[contenteditable="true"]').length ? $('#ContentFrame').contents().find('[contenteditable="true"] p>br') : $('[contenteditable="true"] p>br');
        length += $contentEditable.length;
        if (length >= this.config.maxlength) {
            return false;
        }
        return true;
    },
    notifyPluginConfig: function(pluginConfig) {
        pluginConfig = pluginConfig || {};
        CUI.rte.Utils.applyDefaults(pluginConfig, {
            "maxlength": 0,

        });
        this.config = pluginConfig;
    }

});


//register plugin
CUI.rte.plugins.PluginRegistry.register("customvalidate", CUI.rte.plugins.ValidatorPlugin);


Put this js in a clientlibrary folder with category "cq.authoring.dialog".

After that in your component dialog, use the validator as shown below: