Utilizing strings as array keys

Question

Utilizing strings as array keys

When utilizing strings as keys in an array, the console does not display these declared values when iterating through them, even though the values can still be accessed.

>> var arr = [ 0, 1, 2, 3 ];
   undefined

>> arr["something"] = "aught";
   "aught"

>> arr
   [0, 1, 2, 3]

>> arr["something"]
   "aught"

>> for( var i = arr.length; i--; console.log( arr[ i ] ) );
   3
   2
   1
   0

I've come to understand that arrays are essentially objects with a built-in 'enumerate' interface within JavaScript's engine.

What's most intriguing is that the interpreter doesn't throw any warnings or errors, leading me to spend time searching for where the data could potentially be lost.

javascript arrays

Answer 1

Answer №1

JavaScript offers two types of arrays: standard arrays and associative arrays

[ ] - standard array that uses 0 based integer indexes only
{ } - associative array represented by JavaScript objects where keys can be any strings

When you declare:

var arr = [ 0, 1, 2, 3 ];

You are creating a standard array where indexes must be integers. If you use arr["something"], because something is not an integer value, you are essentially defining a property on the arr object (remember, everything is an object in JavaScript), but you are not adding an element to the standard array.

Answer 2

JavaScript offers two types of arrays: standard arrays and associative arrays

[ ] - standard array that uses 0 based integer indexes only
{ } - associative array represented by JavaScript objects where keys can be any strings

When you declare:

var arr = [ 0, 1, 2, 3 ];

You are creating a standard array where indexes must be integers. If you use arr["something"], because something is not an integer value, you are essentially defining a property on the arr object (remember, everything is an object in JavaScript), but you are not adding an element to the standard array.

Answer 3

Answer №2

for( let counter = arr.length; counter--; console.log( arr[ counter ] ) );

In this code snippet, only the numeric indices are printed. However, you can still iterate over both numeric indices and string keys of the array by using the following loop:

for (let key in arr) {
    console.log(key + ": " + arr[key]);
}
/* This will output:
     0: 0
     1: 1
     2: 2
     3: 3
     something: aught
*/

Answer 4

for( let counter = arr.length; counter--; console.log( arr[ counter ] ) );

In this code snippet, only the numeric indices are printed. However, you can still iterate over both numeric indices and string keys of the array by using the following loop:

for (let key in arr) {
    console.log(key + ": " + arr[key]);
}
/* This will output:
     0: 0
     1: 1
     2: 2
     3: 3
     something: aught
*/

Utilizing strings as array keys

Answer №1

Answer №2

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