CODEWITHSUNDEEP
javascriptarrays
Kalyan
Kalyan

Reputation: 1938

Seeing "undefined" printed when iterating an array

I am iterating a JavaScript array object. I have written a function which iterates the array element. it works but above the result there is written 'undefined'. I don't want to see this, it would be great help to know how to solve this undefine word thing.

var userlist = [{
    "username": "Tom",
    "Current_latitude": 23.752805,
    "Current_longitude": 90.375433,
    "radius": 500
  },

  {
    "username": "Jane",
    "Current_latitude": 23.752805,
    "Current_longitude": 90.375433,
    "radius": 400
  },

  {
    "username": "Dave",
    "Current_latitude": 23.765138,
    "Current_longitude": 90.362601,
    "radius": 450
  }, {
    "username": "Sarah",
    "Current_latitude": 23.792452,
    "Current_longitude": 90.416696,
    "radius": 600
  },

  {
    "username": "John",
    "Current_latitude": 23.863064,
    "Current_longitude": 90.400126,
    "radius": 640
  }
];


var x = Tom(userlist);

function Tom(user) {
  var text;
  for (var i = 0; i < user.length; i++) {
    text += "<li>" + user[i].username + "</li>";
  };
  //text+="</ul>"
  document.getElementById("demo").innerHTML = text;
}

//document.getElementById("demo").innerHTML=userlist[0].username+" "+userlist[0].Current_latitude +  " " + userlist[0].Current_latitude+"" + userlist[0].Current_longitude+" "+ userlist[0].radius;
<p>How to create A javaScript Object Array.</p>
<p id="demo"></p>

Upvotes: 0

Views: 68

Answers (2)

GOTO 0
GOTO 0

Reputation: 47682

You need to initialize your valiable text to an empty string, like this:

var text = "";

Uninitialized variables in JavaScript default to the special value undefined, which is found as text in the concatenation.

As noted in the comments, there's an in issue in your HTML too: <li> tags should only appear inside a containing <ul>, <ol> or <menu> tag. You may consider changing your <li>...</li> to something like <div>...</div> or wrapping the text concatendated text with <ul>...</ul>.

Upvotes: 6

James Thorpe
James Thorpe

Reputation: 32202

It's because you haven't initialised your variable:

var text;  //text is undefined at this point
for (var i = 0; i < user.length; i++) 
{
    //the first iteration of the loop will append to "undefined"
    text+="<li>"+ user[i].username+"</li>";
};

Simply give it an initial value:

var text = '';
for (var i = 0; i < user.length; i++) 
{
    text+="<li>"+ user[i].username+"</li>";
};

As noted by Juhana, however, this isn't generating valid markup. You can uncomment your closing tag, and initialise text to <ul> instead:

var text = '<ul>';
for (var i = 0; i < user.length; i++) 
{
    text+="<li>"+ user[i].username+"</li>";
};
text += "</ul>";

Upvotes: 4

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