How would I create a hyperlink in an email that directs to an iFrame showing a specific item from a list?

I want to make a hyperlink which opens up a modal/iFrame/iDialog or anything that could display a form showing a specific item from an SharePoint Online list. Here's what I've got so far (with help from AmosWu!):

 <IFrameDialog 
    url={this.state.iFrameUrl}
    hidden={false}
    width={'570px'}
    height={'315px'}/>

public getQueryString(name) { 
    var reg = new RegExp("(^|&)" + name + "=([^&]*)(&|$)", "i"); 
    console.log(reg, 'reg');
    var r = window.location.search.substr(1).match(reg); 
    console.log(r, 'r');
    if (r != null) return unescape(r[2]); return null; 
  } 

public componentDidMount() {

    //@ts-ignore
    var iFrameUrl = this.getQueryString("iframe");
    console.log(iFrameUrl, 'iFrameUrl');
    this.setState({
      iFrameUrl: iFrameUrl,
    });

  }

I'm getting undefined for all logs on the above apart from reg.