Xrm WEBAPI Calls as Syncronous sample code using Promise

By default XRm WebAPI are asynchronous and to make this synchronous you can use below code structrure with using Promise.

ValidateZipCode: function (executionContext) {
        "use strict";
        
        var formContext = executionContext.getFormContext();
        var postalcode = formContext.getAttribute(Resident.Fields.address1_postalcode).getValue();
        var message = "Please enter a valid zip code";
        var uniqueId = "cnt_postalcodenotpresent"; 

        return new Promise(function (resolve, reject) {
            Xrm.WebApi.retrieveMultipleRecords("new_postalcodes", "?$select=new_postalcode&$filter=hsg_postalcode eq '" + postalcode + "' ").then(
                function success(result) {                                        
                    var isNotFound = false;  
                    if(result !== undefined)
                    isNotFound = result.entities.length === 0 ? true : false;                       
                        if (isNotFound) {
                        var errorMessage = "Postal Code Mapping is not present for the given postal code"
                        formContext.ui.setFormNotification(errorMessage, "ERROR", uniqueId);                        
                        
                        }
                        else {
                           
                            formContext.ui.clearFormNotification(uniqueId);
                            formContext.data.entity.save();
                            
                        }     
                                    
                                    
                    // return true or false
                    resolve(isNotFound);
                },
                function (error) {
                    reject(error.message);
                    //console.log(error.message);
                }
            );
        });

    }

Hope this helps.