IE issue - Object.keys(value).length not supported

Question

I've been trying to debug some js in Internet Explorer, and I can't figure this one out. Here's the line that is causing the error:

var numberOfColumns = Object.keys(value).length;

And the error is...

Message: Object doesn't support this property or method
Line: 640
Char: 5
Code: 0
URI: xxx

At first I thought it had something to do with the Object.keys(value).length; property, but strangely (for me anyways), the error is at char 5, which is the beginning of the variable name.

Anyways, I have no idea what's going on or how to fix it. Also, if I replace:

var numberOfColumns = Object.keys(value).length;

With ...

var numberOfColumns = 9; // troubleshooting

The error persists. Please help.

Update

jsFiddle added

http://jsfiddle.net/4Rab7/

Answer 1

The keys property is supported in IE >= 9. You are probably testing it in an earlier version. A simple workaround is:

var length = 0;
for(var prop in data){
    if(data.hasOwnProperty(prop))
        length++;
}

Here is a demonstration: http://jsfiddle.net/vKr8a/

See this compatibility table for more info:

http://kangax.github.com/es5-compat-table/

Answer 2

Alternatively, you could use a recommended polyfill for browsers that don't natively support Object.keys

Object.keys=Object.keys||function(o,k,r){r=[];for(k in o)r.hasOwnProperty.call(o,k)&&r.push(k);return r}

A break down of what this script does:

Object.keys = Object.keys || function(o,k,r) { 
// If the script doesn't detect native Object.keys 
// support, it will put a function in its place (polyfill)

    r=[];
    // Initiate the return value, empty array

    for(k in o) r.hasOwnProperty.call(o,k) 
    // loop through all items in the object and verify each
    // key is a property of the object (`for in` will return non 
    // properties)

    && r.push(k);
    // if it is a property, save to return array

    return r
}