So, why does this result in 0 and how do I find the actual size?
var array = [];
array["foo"] = "bar";
array["bar"] = "foo";
document.write(array.length);
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7 Answers
First off, the length is 0 because the number of items in array is 0.
When you do this syntax array["foo"] = "bar" you're creating a property called foo that has a value of bar. The length is still 0 since you have not added anything to the Array, you've just set new properties on the Array
Working version here: http://jsfiddle.net/VyjJD/3/
var array = [];
array["foo"] = "bar";
array["bar"] = "foo";
array.bin = function() { return "bin"; };
array[0] = "bar";
array[1] = "foo";
array[2] = "bin";
array[3] = "bat";
var props = 0;
for (key in array)
props++;
document.write(array.length + "<br />"
+ props + "<br />"
+ (array.foo == array["foo"]) + "<br />"
+ array.bar + "<br />"
+ array.bin());
Notice that array.length = 4 but props = 7 which is all of the properties and the number of items in the Array.
Comments
Since that is a object, which is comprised of properties, and take the form of key/value pairs (conceptually similar to an associative array, or a hash table) you will have to do something like this:
Object.size = function(obj) {
var size = 0, key;
for (key in obj) {
if (obj.hasOwnProperty(key)) size++;
}
return size;
};
var array = [];
array["foo"] = "bar";
array["bar"] = "foo";
var size = Object.size(array);
9 Comments
José Leal
Or also: Object.prototype.size = function()... And then you can use it like: var size = array.size()
karim79
...or as a plain-old function, and just do
getSize(var);
DanMan
There's no such thing as an associative array in JS. It's an object and just an alternative syntax to access it's properties. Instead of
array["foo"] you may as well write array.foo. That's why the length property doesn't work. He's setting properties on an array object and not adding items to an array.
Mantar
@DanMan Fair enough, but how do I find how many properties the array has then?
karim79
@DanMan - But you can think of it as one. In the same way you can call it a 'hash table'. I'm aware that 'properties' can be accessed using both square bracket and dot notation.
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You are setting a property on the array, not giving it a new element. Arrays can receive arbitrary properties, just like any other Javascript object. For instance:
var foo = [];
foo.bar = 'foobar';
console.log(foo.bar); // outputs 'foobar'
console.log(foo); // outputs [] -- empty array
To add items to an array, use Array.push:
var foo = [];
foo.push('foobar');
console.log(foo); // outputs ['foobar']
If you want key=>value pairs, use an object instead:
var foo = {};
foo['bar'] = 'foobar';
console.log(foo); // outputs {bar: 'foobar'}
Comments
basically when you do
array["foo"] = "bar"
it just adds some more attributes to the array, which is an object. In javascript, array.foo and array['foo'] means the same.
2 Comments
Mantar
Thanks for clearing that out. But it doesn't answer the question?
lonesomeday
It doesn't convert it into an object. Arrays are objects, so you can set arbitrary properties on them.
Maybe I'm being naive (my javascript isn't what it might be), but shouldn't it be something like this:
var array = [];
array[0] = "bar";
array[1] = "foo";
document.write(array.length);
Comments
The actual size is 0 because you did not put any items into array object - this can only be done either by a method (push etc.) or by the means of assigning value to an indexed property (or in constructor).
Comments
Object.keys(array).length
see this: https://stackoverflow.com/a/13802999/1488217
credits goes to ian
