gedi/weakmap.js

An evented data API

var WM;

if(typeof WeakMap !== 'undefined'){
    WM = WeakMap;
}else if(typeof window !== 'undefined'){
    var rv = -1; // Return value assumes failure.
    if (navigator.appName == 'Microsoft Internet Explorer'){
        var match = navigator.userAgent.match(/MSIE ([0-9]{1,}[\.0-9]{0,})/);
        if (match && match[1] <= 9){
            WM = require('leak-map');
        }
    }
}

WM || (WM = require('weak-map'));

module.exports = WM;