javascript loop through list items and return the results in an array

Question

I have been trying to loop through an unordered list of numbers with javascript. The function should store all of the numbers in an array so I can find which numbers are duplicates. Any help would be appreciated. So far I have:

    <html>
<head>
    <title></title>
</head>
<body>
<ul id="ul">
    <li>6</li>
    <li>3</li>
    <li>1</li>
    <li>4</li>
    <li>7</li>
    <li>4</li>
    <li>2</li>
    <li>8</li>
    <li>9</li>
    <li>2</li>
</ul>
</body>
</html>

and a start on the javascript:

(function(){

            var nums = document.getElementById("ul");
            var listItem = nums.getElementsByTagName("li");

            var newNums = "";

            var dups = function(){
            for (var i = 0; i < listItem.length; i++){

            }

            }; dups();

            })();

what am I missing?

adeneo · Accepted Answer · 2013-12-12 19:06:25Z

30

var nums = document.getElementById("ul");
var listItem = nums.getElementsByTagName("li");

var newNums = [];

for (var i=0; i < listItem.length; i++) {
    newNums.push( parseInt( listItem[i].innerHTML, 10 ) );
}

FIDDLE

To not get duplicated values you can do

for (var i=0; i < listItem.length; i++) {
    var num = parseInt( listItem[i].innerHTML, 10 );
    if (newNums.indexOf(num) === -1) {
        newNums.push( num );
    }
}

FIDDLE

And to also get an array with the values that appear more than once

var newNums   = [],
    duplicate = [];

for (var i=0; i < listItem.length; i++) {
    var num = parseInt( listItem[i].innerHTML, 10 );
    if (newNums.indexOf(num) === -1) {
        newNums.push( num );
    }else{
        duplicate.push( num );
    }
}

FIDDLE

Array.indexOf might not be supported in all browsers, but there's a polyfill over at MDN

edited Dec 12, 2013 at 19:06

answered Dec 12, 2013 at 19:00

adeneo

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