<aura:attribute name="recordFields" type="Custom_Object__c"/>
<aura:attribute name="recordLoadError" type="String"/>

<force:recordData aura:id="recordLoader"
                 fields="Name,Id,Custom_Field_1__c, Custom_Field_2__c"
                 recordId="{!v.recordId}"
                 targetFields="{!v.recordFields}"
                 targetError="{!v.recordLoadError}""
                 />

var myCustomField = component.get('v.recordFields.Custom_Field_1__c');

component.get('v.recordLoadError')
"No such column 'Custom_Field_1__c' exists on entity 'NAMESPACE__Custom_Object__c'."