解决Flask中Fetch请求后模板无法渲染的问题：理解前后端交互模式

<form id="userinfo" action="/submit" method="POST">
    <div class="search-container">
        <div class="first-child">
            <input type="text" autofocus class="search search-bar" name="street_address" placeholder="Type your address, e.g. 145 Main... " autocomplete="address-line1">   
        </div>
        <div class="second-child">
            <input type="text" class="search child-search" name="apartment" placeholder="Apartment, unit, etc." autocomplete="address-line2">
            <input type="text" class="search child-search" name="city" placeholder="City" required autocomplete="address-level2">
            <input type="text" class="search child-search" name="state" placeholder="State / Region" autocomplete="address-level1" required>
            <input type="text" class="search child-search" name="country" placeholder="Country" autocomplete="country-name" required>
            <input type="text" class="search child-search" name="postal_code" placeholder="Postal Code" autocomplete="postal-code" required>
        </div>  
    </div>
    <button type="submit" class="submit">Search</button>      
</form>

from flask import Flask, render_template, request, jsonify

app = Flask(__name__)

# 假设这里有你的reviews模型和helpers模块，为演示目的已简化
# from . import helpers, reviews 

@app.route("/submit", methods=["POST"])
def submit():
    try:    
        # 从传统的表单提交中获取数据
        street_address = request.form.get("street_address")
        apartment = request.form.get("apartment")
        city = request.form.get("city")
        state = request.form.get("state")
        country = request.form.get("country")
        postal_code = request.form.get("postal_code")

        # 示例：将数据组织成列表或字典进行处理
        data_list = [street_address, apartment, city, state, country, postal_code]

        # 实际应用中，这里会调用helpers.check_format和reviews.query
        # if not helpers.check_format(data_list):
        #     return render_template("error.html", message="Incorrect Data Format")
        # address_search = reviews.query.filter(reviews.address.startswith(data_list[0])).all()

        # 示例数据，模拟数据库查询结果
        address_search = [{"id": 1, "address": f"{street_address}, {city}", "details": "Example result 1"}] 

        print("Traditional POST request processed.")
        # 渲染结果模板，浏览器将导航到此页面
        return render_template("result.html", address_search=address_search, status="OK")

    except Exception as e:
        print("Exception Happened:", str(e))
        # 在异常情况下渲染一个错误页面
        return render_template("error.html", message="An unexpected error occurred.")

document.getElementById('userinfo').addEventListener('submit', function (event) {
  event.preventDefault(); // 阻止表单默认提交行为

  const formData =