Console methods explained

🆒 Console outputs and levels

console.log Normal output to stdout
console.info Normal output to stdout with log level info
console.error Output is displayed at stderr
console.warn Warn output is displayed at stdout with log level warn
console.debug Output to stdout with log level debug

Examples:

console.log('This is a normal log line');
console.info('This is a infomation line');
console.error('This is a error line');
console.warn('This is a warning line');
console.debug('This is a debug line');

🆒 Console utilities

console.clear Clear the console
console.count(label) Log the number of times this line has been called with same label
console.countReset(label) Reset the counter for given label

Example:

console.count('test');
// Output should show: test: 1
console.count('test');
// Output should show: test: 2
console.count('test');
// Output should show: test: 3
console.countReset('test');
console.count('test');
// Output should show: test: 1

console.time(label) Starts a timer to a given label
console.timeLog(label) Show the value of the specified timer label (in miliseconds)
console.timeEnd(label) Stops and show the timer of given label (in miliseconds)

Example:

console.timer('testTimer');
// wait 1 second
console.timerLog('testTimer');
// Output should show: testTimer: 1.000 ms
// and wait 1.5 seconds :P
console.timerEnd('testTimer');
// Output should show: testTimer: 2.500 ms

🆒 Using console to display data

console.dir(object) Display the given object as JSON tree
console.table(object, [columns]) Displays tabular data as a table (Array, Sets...) you can filter what columns you want to show

Examples:

const arrayOfObjects = [
  {
    name: 'one',
    odd: false,
    count: 1,
  },
  {
    name: 'two',
    odd: true,
    count: 2,
  },
  {
    name: 'one',
    odd: false,
    count: 3,
  },
];

// Display as JSON tree
console.dir(arrayOfObjects);

// Output:
// [
//   { name: 'one', odd: false, count: 1 },
//   { name: 'two', odd: true, count: 2 },
//   { name: 'one', odd: false, count: 3 }
// ]

// Render a table with all columns
console.table(arrayOfObjects);

// Output
// ┌─────────┬───────┬───────┬───────┐
// │ (index) │ name  │  odd  │ count │
// ├─────────┼───────┼───────┼───────┤
// │    0    │ 'one' │ false │   1   │
// │    1    │ 'two' │ true  │   2   │
// │    2    │ 'one' │ false │   3   │
// └─────────┴───────┴───────┴───────┘

// Render a table filtering columns
console.table(arrayOfObjects, ['name', 'odd']);

// Output
// ┌─────────┬───────┬───────┐
// │ (index) │ name  │  odd  │
// ├─────────┼───────┼───────┤
// │    0    │ 'one' │ false │
// │    1    │ 'two' │ true  │
// │    2    │ 'one' │ false │
// └─────────┴───────┴───────┘

🆒 Error handling and debug utilities

console.trace( message, object)

const testObject = { awesome: true, boring: false };
console.trace('Trace dump text', testObject );

// Output
Trace: Trace dump text { awesome: true, boring: false }
    at Object.<anonymous> (/code/guidesmiths/js-pills/basic/console-explained/index.js:48:9)
    at Module._compile (internal/modules/cjs/loader.js:1138:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1158:10)
    at Module.load (internal/modules/cjs/loader.js:986:32)
    at Function.Module._load (internal/modules/cjs/loader.js:879:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:71:12)
    at internal/main/run_main_module.js:17:47

console.assert(assertion, message) writes an error message to the console if the assertion is false. If the assertion is true, nothing happens.

const x = 5;
const y = 3;
const reason = `${x} is expected to be less than ${y}`;
console.assert(x < y, reason);

// Output
Assertion failed: 5 is expected to be less than 3

November 18, 2020 - author unknown