alert 与 console.log

var colors = [red, green];
var red = 1;
var green = 444;
console.log(colors);
//VM360:5 [undefined, undefined]
//undefined

var colors = [red, green];
var red = 1;
var green = 444;
alert(colors);
//undefined

//alert在内部会自动调用toString（），而console.log却没有