Why is console.log() considered better than alert()?

Question

I've always been told that when debugging an application, JavaScript's console.log() method is preferred over simply using an alert() method. Why is this? Is there a good example someone can point me to where console.log() is obviously the better choice?

Answer 1

• alert() is blocking
• alert() cannot be easily suppressed in non-debug environment
• console typically formats your objects nicely and allows to traverse them
• logging statements often have an interactive pointer to code which issued logging statement
• you cannot look at more than one alert() message at a time
• consoles can have different logging levels with intuitive formatting

Answer 2

Try this:

var data = {a: 'foo', b: 'bar'}; console.log(data); alert(data); 

You'll see that console.log shows you the object, while alert gives you [object Object], which isn't useful. This is true also of, e.g. elements:

alert(document.body); // [object HTMLBodyElement] (exact result depends on your browser)