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Javascript's arrays cannot be used as maps or associative arrays. Arrays require numeric, consecutive keys. Otherwise it's an Object. -- Clarification edit: C

Javascript's arrays cannot be used as maps or associative arrays. Arrays require numeric, consecutive keys. Otherwise it's an Object. -- Clarification edit: Creating a new key on an array using arr['key']=1 creates a property on the arr Object but does not add an element to the standard array. http://stackoverflow.com/questions/8630471/strings-as-keys-of-array-in-javascript http://stackoverflow.com/questions/8630471/strings-as-keys-o...

mc808 12y ago
Arrays are always objects in JavaScript, and they can be extended like any other object or used as maps (barring key conflicts).
dsp1234 12y ago
Adding non-numeric keys does not remove an Array's "arrayness" in JavaScript var x = []; console.log(Object.prototype.toString.call(x)); //[object Array] x[0] = 1; console.log(x[0]); //1 x["test"] = 2; console.log(x["test"]); //2 console.log(Object.prototype.toString.call(x)); //[object Array] x.map //function map() { [native code] } var y = {}; console.log(Object.prototype.toString.call(y)); //[object Object] y.map //undefined
- the_mitsuhiko 12y ago
  It does internally. Pretty sure that's even defined in the standard.
  - cgrand-net 12y ago
    If you can't observe a difference, does it matter?
  - gsnedders 12y ago
    No, it doesn't. The only magic per spec is about the "length" property (which is essentially a getter/setter pair, despite being a data property and not an accessor pair). That's the only thing special about arrays in JS.
- nothrabannosir 12y ago
  His point was: x = [1]; x["test"] = 555; x.map(function (y) { return y; }); // [1] That's [1], not [1, 555]. You can access the array from the map interface, but not the other way around.
  - dsp1234 12y ago
    The array prototype functions are only specified by the standard to deal solely with numeric keys, but the lines between and object and array are still pretty blurry. The use case for each is different, but the original question far above was "array/map combo. Have you ever seen anything like that in another language?", and clearly JavaScript is very similar even if not exact. var x = {}; x[0] = 1; x.length = 1; x.map = Array.prototype.map; x.map(function(y) {return y;}); //[1]
robocat 12y ago
Arrays are full objects e.g. function(){ var x = []; x.foo = "bar"; return x.foo;} returns "bar". That is the whole reason prototype.js library broke the use of for (var x in somearray) because the library set properties on Array.prototype.

mc808 12y ago

Arrays are always objects in JavaScript, and they can be extended like any other object or used as maps (barring key conflicts).

dsp1234 12y ago

Adding non-numeric keys does not remove an Array's "arrayness" in JavaScript var x = []; console.log(Object.prototype.toString.call(x)); //[object Array] x[0] = 1; console.log(x[0]); //1 x["test"] = 2; console.log(x["test"]); //2 console.log(Object.prototype.toString.call(x)); //[object Array] x.map //function map() { [native code] } var y = {}; console.log(Object.prototype.toString.call(y)); //[object Object] y.map //undefined

the_mitsuhiko 12y ago
It does internally. Pretty sure that's even defined in the standard.
- cgrand-net 12y ago
  If you can't observe a difference, does it matter?
- gsnedders 12y ago
  No, it doesn't. The only magic per spec is about the "length" property (which is essentially a getter/setter pair, despite being a data property and not an accessor pair). That's the only thing special about arrays in JS.
nothrabannosir 12y ago
His point was: x = [1]; x["test"] = 555; x.map(function (y) { return y; }); // [1] That's [1], not [1, 555]. You can access the array from the map interface, but not the other way around.
- dsp1234 12y ago
  The array prototype functions are only specified by the standard to deal solely with numeric keys, but the lines between and object and array are still pretty blurry. The use case for each is different, but the original question far above was "array/map combo. Have you ever seen anything like that in another language?", and clearly JavaScript is very similar even if not exact. var x = {}; x[0] = 1; x.length = 1; x.map = Array.prototype.map; x.map(function(y) {return y;}); //[1]

robocat 12y ago

Arrays are full objects e.g. function(){ var x = []; x.foo = "bar"; return x.foo;} returns "bar". That is the whole reason prototype.js library broke the use of for (var x in somearray) because the library set properties on Array.prototype.