JavaScript Oddities

javascript-oddities.js

// Lack of function signature.
var foo = 'im a number'

function divideByFour(number) {
  return number / 4
}

console.log(divideByFour(foo)) //NaN

// Immutability support.
const array = [3, 6]
array[5] = 9
console.log(array) // [ 3, 6, , , , 9 ]

// Arrays don't have to contain same type of objects.
var array = [0, 1, 2]
array["hello"] = "world"
console.log(array) // [ 0, 1, 2, hello: 'world' ]

// Documentation suggests: It’s best to leave exceptions as a last line of defense,
// for handling the exceptional errors you can’t anticipate, and to manage anticipated
// errors with control flow statements.
function tenDividedBy(number) {
  if (number == 0) {
    throw "can't divide by zero"
  }
  return 10 / number
}

console.log(tenDividedBy(0))
/*
/temp/file.js:9
    throw "can't divide by zero"
    ^
can't divide by zero
*/

// No support for decimals.
console.log(0.1 + 0.2) //0.30000000000000004
console.log(0.1 + 0.2 === 0.3) //false

// Confusing math operations.
var a = 0
var b = -0
console.log(a === b) // true
console.log(1/a === 1/b) // false

var x = Math.sqrt(-2)
console.log(x === NaN) //false
console.log(isNaN(x)) //true
console.log(isNaN('hello world')) //true

// Treatment of null and undefined is confusing:
var foo;
foo === null; //false
foo === undefined; //true