[js tricks] JavaScript tricks, quizes and more tips... #js #javascript #quiz #test #tricks #tips

js-tricks.js

console.log(
  
  // quiz 1: Why is result false?
  "This is a string." instanceof String, // false
  
  // explain quiz 1
  typeof "This is a string.", // "string"
  typeof String, // "object"
  new String("This is a string.") === String, // true
  new String("This is a string.") === Object, // true
  
  // -------

  // quiz 2: Why is result false?
  0.1 + 0.2 === 0.3, // false
  
  // explain quiz 2:
  (0.1 + 0.2), // 0.30000000000000004
  (0.1 + 0.2).toFixed(1), // '0.3'
  Number((0.1 + 0.2).toFixed(1)) === 0.3, // true
  
  // -------
  
  // quiz 3: Result?
  String.raw`HelloTwitter\nworld`, // HelloTwitter\nworld
  // Because the raw method prints exactly what it sees.
  
  // -------
  
  // quiz 4: Result?
  ('b' + 'a' + + 'a' + 'a').toLowerCase(), // banana

  // explain quiz 4
  (+ 'a'), // NaN
  ('a' + + 'a'), // aNaN
  ('b' + 'a' + + 'a' + 'a'), // baNaNa

  // -------
  
  // quiz 5: Why typeof NaN is equal to 'number'?
  typeof NaN === 'number', // true
  
  // explain quiz 5: not a number(NaN) is number but is fake number.
  isNaN(NaN), // true
  isNaN(5), // false
  
  // -------
  
  // quiz 6: Result?
  3 > 2 > 1, // false
  
  // explain quiz 6: Any compiler always starts reading left to right.
  3 > 2, // true
  true > 1, // false because true is equal to 1
  true === 1, // true
  
  // -------
  
  // quiz 7: Explain for Why?
  (() => {
  	let arr = [1, 2, 3];
  	
  	arr[6] = 9; // [1, 2, 3, <3 empty item>, 9]
  
  	return arr[5]
  })() // undefined
  
)