A browser’s debugging console can be used in order to print simple messages. This debugging or web console can be directly opened in the browser (F12 key in most browsers – see Remarks below for further information) and the log method of the console Javascript object can be invoked by typing the following:
console.log('My message');
Then, by pressing Enter, this will display My message in the debugging console.
console.log() can be called with any number of arguments and variables available in the current scope. Multiple arguments will be printed in one line with a small space between them.
var obj = { test: 1 };
console.log(['string'], 1, obj, window);
The log method will display the following in the debugging console:
['string'] 1 Object { test: 1 } Window { /* truncated */ }
Beside plain strings, console.log() can handle other types, like arrays, objects, dates, functions, etc.:
console.log([0, 3, 32, 'a string']);
console.log({ key1: 'value', key2: 'another value'});
Displays:
Array [0, 3, 32, 'a string']
Object { key1: 'value', key2: 'another value'}
Nested objects may be collapsed:
console.log({ key1: 'val', key2: ['one', 'two'], key3: { a: 1, b: 2 } });
Displays:
Object { key1: 'val', key2: Array[2], key3: Object }
Certain types such as Date objects and functions may be displayed differently:
console.log(new Date(0));
console.log(function test(a, b) { return c; });
Displays:
Wed Dec 31 1969 19:00:00 GMT-0500 (Eastern Standard Time)
function test(a, b) { return c; }