mail-addons/mail_recovery/static/src/js/mail_recovery.js

odoo.define('mail_recovery', function (require) {
    var composer = require('mail.composer');

    composer.BasicComposer.include({
        init: function(){
            this._super.apply(this, arguments);
            this.events['focus .o_composer_input textarea'] = 'on_focus_textarea';
            this.events['keyup .o_composer_input textarea'] = 'on_keyup_textarea';
        },
        on_focus_textarea: function(event) {
            var $input = $(event.target);
            if (!$input.val()) {
                $input.val(window.localStorage.message_storage);
            }
        },
        on_keyup_textarea: function(event) {
            window.localStorage.message_storage = $(event.target).val();
        },
        send_message: function (event) {
            window.localStorage.message_storage = '';
            return this._super(event);
        },
    });
});