Comment by krackers

17 hours ago

Actually in JS array indexing is same as property indexing right? So it's actually looking up the string '0', as in arr['0']

4 comments

krackers

idle_zealot 17 hours ago

Huh. I always thought that JS objects supported string and number keys separately, like lua. Nope!

  [Documents]$ cat test.js
  let testArray = [];
  testArray[0] = "foo";
  testArray["0"] = "bar";
  console.log(testArray[0]);
  console.log(testArray["0"]);
  [Documents]$ jsc test.js
  bar bar
  [Documents]$

nvlled 11 hours ago

Lua supports even functions and objects as keys:

  function f1() end
  function f2() end
  local m1 = {}
  local m2 = {}
  local obj = {
      [f1] = 1,
      [f2] = 2,
      [m1] = 3,
      [m2] = 4,
  }
  print(obj[f1], obj[f2], obj[m1], obj[m2], obj[{}])

Functions as keys is handy when implementing a quick pub/sub.

aidenn0 16 hours ago
They do, but strings that are numbers will be reinterpreted as numbers.
[edit]
let testArray = []; testArray[0] = "foo"; testArray["0"] = "bar"; testArray["00"] = "baz"; console.log(testArray[0]); console.log(testArray["0"]); console.log(testArray["00"]);
- minitech 16 hours ago
  
  That example only shows the opposite of what it sounds like you’re saying, although you could be getting at a few different true things. Anyway:
  - Every property access in JavaScript is semantically coerced to a string (or a symbol, as of ES6). All property keys are semantically either strings or symbols.
  - Property names that are the ToString() of a 31-bit unsigned integer are considered indexes for the purposes of the following two behaviours:
  - For arrays, indexes are the elements of the array. They’re the properties that can affect its `length` and are acted on by array methods.
  - Indexes are ordered in numeric order before other properties. Other properties are in creation order. (In some even nicher cases, property order is implementation-defined.)
  { let a = {}; a['1'] = 5; a['0'] = 6; Object.keys(a) } // ['0', '1'] { let a = {}; a['1'] = 5; a['00'] = 6; Object.keys(a) } // ['1', '00']