CODEWITHSUNDEEP
javascriptinternet-explorerdom
Saul
Saul

Reputation: 18041

for..in statement not supported for XML DOM childNodes in IE9?

We're developing a javascript-based GIS application and everything was going fine until someone decided to fire up IE9 and gave it a spin over there too. As you have probably already guessed, the app broke down.

Turned out that for some inexplicable reason for..in loop is unable to iterate over childNodes: 

var xmldoc = new ActiveXObject("Msxml2.DOMDocument.6.0");
xmldoc.loadXML("<i18n><item>one</item><item>two</item></i18n>");

var currentItem = xmldoc.getElementsByTagName("i18n")[0].firstChild;

while (currentItem) {
    if (currentItem.nodeType == 1) {
        for (var i in currentItem.childNodes) {
            console.log(currentItem.childNodes[i]);
        }
    }
    currentItem = currentItem.nextSibling;
}

However, when the internal for loop in above code is replaced with

for (var j = 0; j < currentItem.childNodes.length; j++) {
    console.log(currentItem.childNodes[j]);
}

everything works as expected - it walks the child nodes without any issues.

Although I discovered a workaround, the issue still annoys me as it is not clear why it happens. MSDN documentation both for XMLDocument and for..in mentions nothing.

Is this a bug or another case of poorly-documented oddness that IE is famous of?

Upvotes: 0

Views: 309

Answers (2)

Spudley
Spudley

Reputation: 168685

Short answer: Don't use for..in to iterate arrays. Arrays should always be iterated with a for() loop. Only non-array objects should use for...in.

If you must use a for..in here, you should filter the loop using .hasOwnProperty() to prevent unwanted iterations on properties that belong to the array prototype rather than the array itself.

This point applies to all for..in loops: to ensure your code is robust, you should get into the habit of always filtering them with .hasOwnProperty(), even on plain objects, but especially on arrays, since we already know they contain additional properties.

See here for more on this point.

Upvotes: 2

Esailija
Esailija

Reputation: 140220

Well, it's not a bug since DOM spec doesn't define that there should be numeric properties, just the item method which [] desugars to.

Simply don't use for..in.

Upvotes: 2

Related Questions