无法使用“this.refname.current”从useEffect访问Ref

我这里缺少一些简单的东西,我需要访问 useEffect 。调试器显示 this 是未定义的,因此我不能 this.refOverlay.current; .

// Ref
const refOverlay = useRef(null); 

// Sample useEffect that references it
useEffect(() => {
    if (props.mode === 'new') {
        let b = this; // Undefined
        let a = this.refOverlay.current; // Error on this line
        if (a) {
            console.log('ok');
        }
    }
}, [props.mode]);

...
return (
{/* JSX Definition */}
        <OverlayTrigger ref={refOverlay} trigger="click" rootClose placement="bottom" overlay={popoverApprover}>
            <a href="javascript:void(0)" className="more-info">TEST</a>
        </OverlayTrigger> 
);