Regarding the delegate problem of jq

<code>//PHP
<?php
include "db.php";
if(isset($_POST["category"])){


    $category_query = "SELECT * FROM categories";


    $run_query = mysqli_query($con,$category_query); 
    echo "
<div class='nav nav-pills nav-stacked'>
    <li class='active'><a href='#'><h4>Categories</h4></a></li>
    ";

    if(mysqli_num_rows($run_query)>0){
        
        while($row = mysqli_fetch_array($run_query)){
            $cid = $row["cat_id"];
            $cat_name = $row["cat_title"];

//问题在这里
            echo "
<li><a href='#' class='category' cid='$cid'>$cat_name</a></li>
            ";
        }
        echo "</div>";
    }
}


if(isset($_POST["brand"])){
    $brand_query = "SELECT * FROM brands";
    $run_query = mysqli_query($con,$brand_query);
    echo "
<div class='nav nav-pills nav-stacked'>
    <li class='active'><a href='#'><h4>Brands</h4></a></li>
    ";

    if(mysqli_num_rows($run_query)>0){
        while($row = mysqli_fetch_array($run_query)){
            $bid = $row["brand_id"];
            $brand_name = $row["brand_title"];
            echo "
<li><a href='#'>$brand_name</a></li>
            ";
        }
        echo "</div>";
    }
}

if(isset($_POST["getProduct"])){
    $product_query =  "SELECT * FROM products ORDER BY RAND() LIMIT 0,9";
    $run_query = mysqli_query($con,$product_query);
    if(mysqli_num_rows($run_query) >0 ){
        while($row = mysqli_fetch_array($run_query)){
           $pro_id = $row['product_id'];
           $pro_cat = $row['product_cat'];
           $pro_brand = $row['product_brand'];
           $pro_title = $row['product_title'];
           $pro_price = $row['product_price'];
           $pro_image = $row['product_image'];
           echo "
             <div class='col-md-4'>
                        <div class='panel panel-info'>
                            <div class='panel-heading'>$pro_title</div>
                            <div class='panel-body'>
                                <img style='width:300px;height:300px' src='product_image/$pro_image' />
                            </div>
                            <div class='panel-heading'>$.$pro_price.00
                              <button pid='$pro_id' style='float:right' class='btn btn-danger btn-xs'>AddToCart</button>
                            </div>
                        </div>
                        </div>
           ";
        }
    }

}


?></code>

<code>//JS

 $(document).ready(function() {
    cat();
    brand();
    product();

    function cat() {
        $.ajax({
                url: 'action.php',
                type: 'POST',
                data: {
                    category: 1
                },
            })
            .done(function(data) {
                //console.log(data);
                $("#get_category").html(data);

            });


    }

    function brand() {
        $.ajax({
                url: 'action.php',
                type: 'POST',
                data: {
                    brand: 1
                },
            })
            .done(function(data) {
                //console.log(data);

                $("#get_brand").html(data);

            });


    }


    function product() {
        $.ajax({
                url: 'action.php',
                type: 'POST',
                data: {
                    getProduct: 1
                },
            })
            .done(function(data) {
                //console.log(data);
                $("#get_product").html(data);

            });
    }

    //使用 delegate() 方法。on不能获取
    $("body").delegate(".category", "click", function() {
        alert(123);
    })
    // $(".category").on("click", function(event) {
    //     alert(13);
    // });
})</code>

Why is there no response when clicking when I use the on method? But the delegate does? Is it because this class is written in PHP and cannot be read by on? Or what?

Reply content:

<code>//PHP
<?php
include "db.php";
if(isset($_POST["category"])){


    $category_query = "SELECT * FROM categories";


    $run_query = mysqli_query($con,$category_query); 
    echo "
<div class='nav nav-pills nav-stacked'>
    <li class='active'><a href='#'><h4>Categories</h4></a></li>
    ";

    if(mysqli_num_rows($run_query)>0){
        
        while($row = mysqli_fetch_array($run_query)){
            $cid = $row["cat_id"];
            $cat_name = $row["cat_title"];

//问题在这里
            echo "
<li><a href='#' class='category' cid='$cid'>$cat_name</a></li>
            ";
        }
        echo "</div>";
    }
}


if(isset($_POST["brand"])){
    $brand_query = "SELECT * FROM brands";
    $run_query = mysqli_query($con,$brand_query);
    echo "
<div class='nav nav-pills nav-stacked'>
    <li class='active'><a href='#'><h4>Brands</h4></a></li>
    ";

    if(mysqli_num_rows($run_query)>0){
        while($row = mysqli_fetch_array($run_query)){
            $bid = $row["brand_id"];
            $brand_name = $row["brand_title"];
            echo "
<li><a href='#'>$brand_name</a></li>
            ";
        }
        echo "</div>";
    }
}

if(isset($_POST["getProduct"])){
    $product_query =  "SELECT * FROM products ORDER BY RAND() LIMIT 0,9";
    $run_query = mysqli_query($con,$product_query);
    if(mysqli_num_rows($run_query) >0 ){
        while($row = mysqli_fetch_array($run_query)){
           $pro_id = $row['product_id'];
           $pro_cat = $row['product_cat'];
           $pro_brand = $row['product_brand'];
           $pro_title = $row['product_title'];
           $pro_price = $row['product_price'];
           $pro_image = $row['product_image'];
           echo "
             <div class='col-md-4'>
                        <div class='panel panel-info'>
                            <div class='panel-heading'>$pro_title</div>
                            <div class='panel-body'>
                                <img style='width:300px;height:300px' src='product_image/$pro_image' />
                            </div>
                            <div class='panel-heading'>$.$pro_price.00
                              <button pid='$pro_id' style='float:right' class='btn btn-danger btn-xs'>AddToCart</button>
                            </div>
                        </div>
                        </div>
           ";
        }
    }

}


?></code>

<code>//JS

 $(document).ready(function() {
    cat();
    brand();
    product();

    function cat() {
        $.ajax({
                url: 'action.php',
                type: 'POST',
                data: {
                    category: 1
                },
            })
            .done(function(data) {
                //console.log(data);
                $("#get_category").html(data);

            });


    }

    function brand() {
        $.ajax({
                url: 'action.php',
                type: 'POST',
                data: {
                    brand: 1
                },
            })
            .done(function(data) {
                //console.log(data);

                $("#get_brand").html(data);

            });


    }


    function product() {
        $.ajax({
                url: 'action.php',
                type: 'POST',
                data: {
                    getProduct: 1
                },
            })
            .done(function(data) {
                //console.log(data);
                $("#get_product").html(data);

            });
    }

    //使用 delegate() 方法。on不能获取
    $("body").delegate(".category", "click", function() {
        alert(123);
    })
    // $(".category").on("click", function(event) {
    //     alert(13);
    // });
})</code>

Why is there no response when I click on the on method? But delegate does? Is it because this class is written in PHP and cannot be read by on? Or what?

Use on

for dynamically generated elements

<code> $('body').on('click','.category' , function() {
         alert(123);
     })</code>

Before you use a new API, you should fully understand its function through the documentation.