primitive-and-operators.js

'use strict';

// first line of the file must be 'use strict' to ensure we use javascript
// in strict mode

// lines starting with two slashes are comments.
// Comments allow you to annotate your code with text that will be ignored
// by javascript, it's for keep notes and help too clarify code

/* To avoid adding // before each lines
  Multiline comments start with slash-star,
  and end with star-slash
*/

/*
  Primitives and operators
*/

// Booleans are the simplest type
console.log(true);
console.log(false);

// Numbers
console.log(42);
console.log(21 + 21);
console.log(21 * 2);
console.log(84 / 2);
console.log(1042 % 50);
console.log(2.1 * 10 + 21);
console.log(4.2 * (5 + 5)); // Precedence is enforced with parentheses.

// Strings are with ', " or `
console.log('Hello World!');
console.log("I'm such a nice boy"); // but you may use " if your string contains '

// if you need to have a quote in a string you can escape it with a backslash \
console.log('It\'s time to escape!!');
console.log('Hello' + 'World!');
console.log('Hello\nWorld!');
console.log(`Hello
World!`);

// There's also `null` and `undefined`.
console.log(null); // used to indicate a deliberate non-value
console.log(undefined); // used to indicate a value is not currently present
// (although `undefined` is actually a value itself)

// You may mix types, but results may not be what you expect
console.log('21' + 21);
console.log('21' * 2);
console.log('21' * true); // true is cooerced to be the number 1
console.log('21' * false); // false become the number 0

// When javascript can't compute a number it returns NaN (stands for 'Not a Number')
console.log(NaN);
console.log('21' * 'tomato');

// Infinity is another special number
console.log(Infinity);
console.log(1 / 0);
console.log(-Infinity); // it can be negative
console.log(-1 / 0);

// Comparaisons always return a boolean :

// Equality is ===
console.log(1 === 1); // true
console.log(1 === 2); // false

// Inequality is !==
console.log(1 !== 1); // = false
console.log(1 !== 2); // = true

// You can use the Negation ! symbol to get the inverse boolean of any value
console.log(!true); // = false
console.log(!false); // = true

// Greater than and lesser than
console.log(1 < 10); // = true
console.log(1 > 10); // = false
console.log(2 <= 2); // = true
console.log(2 >= 2); // = true

// and it works for strings
console.log('a' < 'b'); // = true
console.log('aba' < 'abc'); // = true

// THE MORE YOU KNOW :

// Non boolean values are either 'truthy' or 'falsy'
console.log(!0); // = true
console.log(!1); // = false
console.log(!123); // = false
console.log(!''); // = true
console.log(!'tomato'); // = false

// Type coercion is performed for comparisons with double equals...
console.log('5' == 5); // = true
console.log(undefined == null); // = true

// ...avoid loosing your hairs and you use the strict === instead... please...
console.log('5' === 5); // = false
console.log(undefined === null); // = false

// JavaScript has one number type (which is a 64-bit IEEE 754 double).
// Doubles have a 52-bit mantissa, which is enough to store integers
// up to about 9✕10¹⁵ precisely.

// Float have limited precision, this is why :
console.log(0.1 + 0.2); // is not precisly 0.3 but 0.30000000000000004