A simple, annotated forEach function

forEach.js

var forEach = function(obj, cb, context){
    // check for a native forEach function
    var native = [].forEach,
        hasProp = Object.prototype.hasOwnProperty;
    
    // if there is a native function, use it
    if (native && obj.forEach === native) {
        //don't bother if there is no function
        cb && obj.forEach(cb, context);
    }
    // if the object is array-like
    else if (obj.length === +obj.length) {
        // loop though all values
        for (var i = 0, length = obj.length; i < length; i++) {
            // call the function with the context and native-like arguments
            cb && cb.call(context, obj[i], i, obj);
        }
    }
    // it's an object, use the keys
    else {
        // loop through all keys
        for (var name in obj){
            // call the function with context and native-like arguments
            if (hasProp.call(obj, name)) {
                cb && cb.call(context, obj[name], name, obj);
            }
        }
    }
};