遺漏的類型錯誤：不能爲空

Question

我得到這個遺漏的類型錯誤「上」讀取屬性：

我不能確定是什麼原因造成，maybes事做與jQuery？

這裏是確切的代碼：

//when add to cart link is clicked... 
$('.addtocart').on('click', function(){ 

    //get the value of the "data-value" attribute for that link 
    var vehicleRegistration = $(this).data('value'); 
    //save it to localStorage 
    localStorage.setItem('vehicleRegistration', vehicleRegistration); 


    //read from localStorage 
    if(localStorage.getItem('vehicleRegistration')){ 
    //add the value to the form input 
    $('#field34').val(localStorage.getItem('vehicleRegistration')); 
    } 

}); 

這裏是它發生在頁面：http://drivencarsales.co.uk/book-testdrive

這真是難住我了，如果有人能幫助我解決這個問題，將不勝感激。

謝謝，尼克

Answer 1

在你的網站，你有兩個prototype.js和jQuery增加。 $這裏調用prototype.js而不是jQuery。因此，而不是代碼，請其更改爲：

jQuery('.addtocart').on('click', function(){ 

    //get the value of the "data-value" attribute for that link 
    var vehicleRegistration = jQuery(this).data('value'); 
    //save it to localStorage 
    localStorage.setItem('vehicleRegistration', vehicleRegistration); 


    //read from localStorage 
    if(localStorage.getItem('vehicleRegistration')){ 
    //add the value to the form input 
    jQuery('#field34').val(localStorage.getItem('vehicleRegistration')); 
    } 

}); 

或者你也可以這樣做：

(function ($) { 
    $('.addtocart').on('click', function(){ 

     //get the value of the "data-value" attribute for that link 
     var vehicleRegistration = $(this).data('value'); 
     //save it to localStorage 
     localStorage.setItem('vehicleRegistration', vehicleRegistration); 


     //read from localStorage 
     if(localStorage.getItem('vehicleRegistration')){ 
     //add the value to the form input 
     $('#field34').val(localStorage.getItem('vehicleRegistration')); 
     } 

    }); 
})(jQuery); 

Answer 2

問題是與$。您的$與jQuery和prototypejs發生衝突。

每當你寫jQuery代碼，嘗試使用自調用函數與jQuery作爲參數。例如：

(function($){//You can use any character instead $ here. 
//Your code here to use $. 
})(jQuery); 

或另一種方式是使用jQuery字代替$。例如：

jQuery('.addtocart').on('click', function(){ 
    //Your code here. 
}); 

在你的代碼，$由原型中使用，因爲當腳本執行有帶班.addtocart沒有元素$('.addtocart')被返回null。這就是爲什麼它在訪問null *（$（'。addtocart'））*時拋出錯誤。

如果你想添加jQuery的唯一事件處理程序。然後用jQuery word代替$。

//when add to cart link is clicked... 
jQuery('.addtocart').on('click', function(){ 

    //get the value of the "data-value" attribute for that link 
    var vehicleRegistration = jQuery(this).data('value'); 
    //save it to localStorage 
    localStorage.setItem('vehicleRegistration', vehicleRegistration); 


    //read from localStorage 
    if(localStorage.getItem('vehicleRegistration')){ 
    //add the value to the form input 
    jQuery('#field34').val(localStorage.getItem('vehicleRegistration')); 
    } 

});