JAVASCRIPT初学者问题

// A simple function for sending a message
function sendMessage( msg, obj ) {
// If both a message and an object are provided
if ( arguments.length == 2 )
// Send the message to the object
obj.handleMsg( msg );
// Otherwise, assume that only a message was provided
else
// So just display the default error message
alert( msg );
}
// Call the function with one argument – displaying the message using an alert
sendMessage( "Hello, World!" );
// Otherwise, we can pass in our own object that handles
// a different way of displaying information
sendMessage( "How are you?", {
handleMsg: function( msg ) {
alert( "This is a custom message: " + msg );
}
});
// A function that takes any number of arguments and makes
// an array out of them
function makeArray() {
// The temporary array
var arr = [];
// Go through each of the submitted arguments
for ( var i = 0; i < arguments.length; i++ ) {
arr.push( arguments[i] );
}
// Return the resulting array
return arr;
}

其中有一段
sendMessage( "How are you?", {
handleMsg: function( msg ) {
alert( "This is a custom message: " + msg );
}
});

这段的语法看不太懂,请人详细解释一下,第二个参数的定义语法和过程,另外