Инспектор консольных сообщений JavaScript
console.log() // outputs a message to the web console
console.assert() // writes an error message to the console if the assertion is false. If the assertion is true, nothing happens.
console.table() // displays tabular data as a table.
console.info() // outputs an informational message to the Web console.
console.error() // outputs an error message to the Web console.
Tommy