Javascript 为什么我总是从 Chrome 收到“Uncaught SyntaxError: Unexpected token u ”？

Why I always get "Uncaught SyntaxError: Unexpected token u " from Chrome?

提问by Dennisboys

I have spent a whole day on this, googling and searching for answers but still could not figure out.

我花了一整天的时间，谷歌搜索并寻找答案，但仍然无法弄清楚。

My code is a bit long and it works well in Firefox but gets "Uncaught SyntaxError: Unexpected token u " from Chrome.

我的代码有点长，它在 Firefox 中运行良好，但从 Chrome 获取“Uncaught SyntaxError: Unexpected token u”。

Can anyone points me out where I am wrong? Thanks in advance!

谁能指出我错在哪里？提前致谢！

// when the page loads, list all the current contacts
$(document).ready(function(){

    // check if localStorage database exists
    if(!localStorage.getItem("customerDatabase")){

        // define a JSON object to hold all current address
        var contacts = {
            "users":[
                {
                    "id":"1",
                    "name":"dennis",
                    "email":"[email protected]"
                },
                {
                    "id":"2",
                    "name":"zoe",
                    "email":"[email protected]"             
                }
            ]   
        } // end of contacts JSON object

        // stringify the object 
        var stringObject = JSON.stringify(contacts);                

        // store it into localStorage database
        var storedDatabase = localStorage.setItem("customerDatabase", stringObject);                                            

    } else {
        // list all customers upon page loads
        listJSONCustomers();        
    }   

    // list all current contacts from JSON object in localStorage
    function listJSONCustomers(){

      var displayHTML = "";
      var i;

      // get the data from localStorage
      var storedDatabase = localStorage.getItem("customerDatabase");

      // parse the data from string to JSON object
      var parseObject = JSON.parse(storedDatabase); 

      // access the users key of the JSON object
      var userObject = parseObject.users;

      // get the length of the object (how many customers the database has)
      var contactsLength = userObject.length;     

      for(i=0; i<contactsLength; i++){
          var trElement = '<tr id="address' + (i+1) + '">';
          var tdId = '<td id="id' + (i+1) + '">' + userObject[i].id + '</td>';
          var tdName = '<td id="name' + (i+1) + '">' + userObject[i].name + '</td>';
          var tdEmail = '<td id="email' + (i+1) + '">' + userObject[i].email + '</td>';
          var tdButton = '<td id="button"><button id="editButton' + userObject[i].id + '">Edit</button> | <button id="deleteButton' + userObject[i].id + '">Delete</button></td>';

          displayHTML += trElement + tdId + tdName + tdEmail + tdButton + '</tr>';
      }     

      $('#address_list').html(displayHTML);           
    }       

    // add customer to database  
    $('#saveCustomer').click(function(){

       if( $('#customerName').val() !== "" && $('#customerEmail').val() !== "" ){

           var customerName = $('#customerName').val();
           var customerEmail = $('#customerEmail').val();

           // get the data from localStorage
           var storedDatabase = localStorage.getItem("customerDatabase");

           // parse the data from string to JSON object
           var parseObject = JSON.parse(storedDatabase);    

           // access the users key of the JSON object
           var userObject = parseObject.users;     

           // get the new entry
           var newCustomerObject = {
                                  "id": userObject.length + 1,
                                  "name": customerName,
                                  "email": customerEmail
                                  };

           // push the new entry into the object                                                            
           userObject.push(newCustomerObject);

           // convert the object into string for localStorage
           var stringObject = JSON.stringify(parseObject);         

           // store the JSON object into localStorage
           var storedDatabase = localStorage.setItem("customerDatabase", stringObject);

           // list all customes again every time a database receives a new entry
           listJSONCustomers();     

       } else {
          alert("Please enter customer's name and email.");  
       }

    }); // end of $('#saveCustomer').click();


});

回答by loganfsmyth

At some point, something you did corrupted the value of your LocalStorage for that key. LocalStorage can only store strings, so if you pass anything else to it, it will convert it to a string. Since your value is 'undefined', that means that at some point, you probably did something like this on accident:

在某些时候，您所做的某些事情破坏了该键的 LocalStorage 值。LocalStorage 只能存储字符串，因此如果您向它传递任何其他内容，它会将其转换为字符串。由于您的值是'undefined'，这意味着在某些时候，您可能不小心做了这样的事情：

var value;
localStorage.setItem('key', value);

In this case, valueis undefined, which is not a string. When this gets saved, it will be converted however. Unfortunately, "undefined"is not valid JSON. That means that when it tries to parse, it will throw an exception.

在这种情况下，valueis undefined，它不是字符串。保存后，它将被转换。不幸的是，"undefined"不是有效的 JSON。这意味着当它尝试解析时，它会抛出异常。

To fix your issue, you should clear the bad value out with removeItem.

要解决您的问题，您应该使用removeItem.

localStorage.removeItem("customerDatabase");