Golang中如何检查元素是否存在并获取其布尔值

Golang中如何检查元素是否存在并获取其布尔值 在我的代码中，我将一个结构体 ReturnedResult 发送到模板：

type ReturnedResult struct {
	Result  bool   `json:"result"`
	Message string `json:"message"`
}

我希望模板能够：

1. 检查是否存在 Result 或为 nil
2. 如果存在 Result，我希望检查它是 true 还是 false

因此，我写了以下代码：

{{with .Result}}
  {{if .Result}}
    <div id='foo'>
      <i class="far fa-thumbs-up"></i>If report not opened automatically, pls download from <a href={{.Message}}>here</a>
    </div>
    <script>
      url = `{{.Message}}`
      window.open(url, "_blank");
      setTimeout(function () {document.querySelector('#foo').style.display='none'}, 5000);
    </script>
  {{else}}
    <i class="fas fa-exclamation-triangle">{{.Message}}</i>>
    <script>
      setTimeout(function () {document.querySelector('#foo').style.display='none'}, 5000);
    </script>
  {{end}}
{{end}}

有时我调用模板时不带数据，如 tmpl.Execute(w, nil)，有时带数据，如 tmpl.Execute(w, webReturn)。

不带数据的调用工作正常，但带数据的调用不工作，不知道问题出在哪里。

如果需要，下面是我的完整代码。

// go build -ldflags "-H=windowsgui"
package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"strings"
	"text/template"

	"github.com/zserge/lorca"
)

// ContactDetails ...
type ContactDetails struct {
	Email   string
	Subject string
	Message string
	Color1  []string
	Color2  []string
}

// ReturnedResult ...
type ReturnedResult struct {
	Result  bool   `json:"result"`
	Message string `json:"message"`
}

func index(w http.ResponseWriter, r *http.Request) {
	tmpl := template.Must(template.ParseFiles("forms.html"))
	if r.Method != http.MethodPost {
		tmpl.Execute(w, nil)
		return
	}

	r.ParseForm()
	fmt.Println(r.Form) // print information on server side.
	fmt.Println("path", r.URL.Path)
	fmt.Println("scheme", r.URL.Scheme)
	fmt.Println(r.Form["color1"][0])
	fmt.Println(r.Form["color1"][1])
	for k, v := range r.Form {
		fmt.Println("key:", k)
		fmt.Println("val:", strings.Join(v, ""))
	}
	details := ContactDetails{
		Email:   r.FormValue("email"),
		Subject: r.FormValue("subject"),
		Message: r.FormValue("message"),
		Color1:  r.Form["color1"],
		Color2:  r.Form["color2"],
	}
	fmt.Printf("Post from website! r.PostFrom = %v\n", r.PostForm)
	fmt.Printf("Details = %v\n", details)

	//r.FormValue("username")
	fmt.Println()
	// do something with details
	sheetID := "AKfycbxfMucXOzX15tfU4errRSAa9IzuTRbHzvUdRxzzeYnNA8Ynz8LJuBuaMA/exec"
	url := "https://script.google.com/macros/s/" + sheetID + "/exec"
	bytesRepresentation, err := json.Marshal(details)
	if err != nil {
		log.Fatalln(err)
	}
	resp, err := http.Post(url, "application/json", bytes.NewBuffer(bytesRepresentation))
	if err != nil {
		log.Fatalln(err)
	}
	// read all response body
	data, _ := ioutil.ReadAll(resp.Body)

	// close response body
	resp.Body.Close()

	webReturn := ReturnedResult{}
	if err := json.Unmarshal([]byte(data), &webReturn); err != nil {
		panic(err)
	}
	fmt.Println(webReturn.Message)

	webReturn.Message = strings.ReplaceAll(webReturn.Message, "&export=download", "")
	//tmpl.Execute(w, struct{ Success bool }{webReturn.Result})
	tmpl.Execute(w, webReturn)
}

func main() {
	// Start Host goroutine
	go func() {
		http.Handle("/static/", http.StripPrefix("/static/", http.FileServer(http.Dir("./public"))))
		http.HandleFunc("/", index)
		http.ListenAndServe(":8090", nil)
	}()

	// Start UI
	ui, err := lorca.New("http://localhost:8090/index", "", 1200, 800)
	if err != nil {
		log.Fatal(err)
	}
	defer ui.Close()

	<-ui.Done()
}

模板：

<title>Form Submittal</title>
<style>
  body {
      font-family: Ubuntu, "times new roman", times, roman, serif;
  }
</style>
<link href="http://localhost:8090/static/fontawesome-free-5.15.2-web/css/all.css" rel="stylesheet"> <!--load all styles -->
<!-- link rel="stylesheet" href="http://localhost:8090/styles/MaterialDesign-Webfont-master/css/materialdesignicons.min.css" -->

<script type="module" src="http://localhost:8090/static/node_modules/@mdi/js/mdi.js"></script>
<script type="module">
 // import {mdi-home} from "./node_modules/@mdi/js/mdi.js";
 // alert(a);
</script>
<script>
  //import { mdi-home } from '/MaterialDesign-JS-master/mdi.js';
  function deleteRow(row) {
    var i = row.parentNode.parentNode.rowIndex - 2; // this -> td -> tr // -2 because the first 2 rows are used for header
    var tbl = document.querySelector('tbody');
    if(tbl && tbl.rows.length > 1) {
      tbl.deleteRow(i); 
      Array.from(tbl.rows).forEach((row, index) => {
        row.cells[0].innerHTML = index + 1;
      });
    }
  } 

  function insRow(row) {
    var i = row.parentNode.parentNode.rowIndex - 2; // this -> td -> tr // -2 because the first 2 rows are used for header
    var tbl = document.querySelector('tbody');
    var row = document.createElement('tr');
    row.innerHTML=`
      <th></th>
      <td><input size=25 type="text" name="color1" /></td>
      <td><input size=25 type="text" name="color2" ></td>
      <td><i class="fas fa-edit" onclick="insRow(this)"></i></td>
      <td><i class="fas fa-eraser" onclick="deleteRow(this)"></i></td>
    `;
    var len = tbl.rows.length;
    row.cells[0].innerHTML = len + 1;
    tbl.insertBefore(row, tbl.children[i+1]);
    Array.from(tbl.rows).forEach((row, index) => {
      row.cells[0].innerHTML = index + 1;
    });
    //tbl.appendChild(row);
  }
</script>
<h1>Contact</h1>
Bob lives in a <span class="mdi mdi-home"></span>.

<form method="POST">
    <label>Email:</label><br />
    <input type="text" name="email"><br />
    <label>Subject:</label><br />
    <input type="text" name="subject"><br />
    <label>Message:</label><br />
    <textarea name="message"></textarea><br />

    <table>
      <caption>Monthly savings</caption>
      <thead>
        <tr>
          <th colspan="5">The table header</th>
        </tr>
        <tr>
          <th>SN</td>
          <th>PO number</td>
          <th>PO invoice value</td>
          <th colspan="2">Action</td>
        </tr>
      </thead>
      <tbody >
        <tr>
          <th>1</th>
          <td><input size=25 type="text" name="color1" /></td>
          <td><input size=25 type="text" name="color2" /></td>
          <td colspan="2"><i class="fas fa-edit" onclick="insRow(this)"></i></td>
        </tr>
      </tbody>
      <tfoot>
        <tr>
          <th colspan="5">The table footer</th>
        </tr>
      </tfoot>
    </table>

   <input type="submit">
</form>
{{with .Message}}
  {{if .Result}}
    <div id='foo'>
      <i class="far fa-thumbs-up"></i>If report not opened automatically, pls download from <a href={{.Message}}>here</a>
    </div>
    <script>
      url = `{{.Message}}`
      window.open(url, "_blank");
      setTimeout(function () {document.querySelector('#foo').style.display='none'}, 5000);
    </script>
  {{else}}
    <i class="fas fa-exclamation-triangle">{{.Message}}</i>>
    <script>
      setTimeout(function () {document.querySelector('#foo').style.display='none'}, 5000);
    </script>
  {{end}}
{{end}}