length of a property in JavaScript object [duplicate]

What is the difference between the two?

So I know that array.size() is a function while array.length is a property. Is there a usecase for using one over the other? Is one more efficient? (I would imagine .length to be significantly faster as it is a property rather then a method call?) Why would one ever use the slower option? Are there some browsers that are incompatible with one or the other?

  var x = [];
  console.log(x.size());
  console.log(x.length);
  console.log(x.size()==x.length);
  x =[1,2,3];
  console.log(x.size());
  console.log(x.length);
  console.log(x.size()==x.length);

Will print:

  0, 0, true
  3, 3, true

Array.size() is not a valid method

Always use the length property

There is a library or script adding the size method to the array prototype since this is not a native array method. This is commonly done to add support for a custom getter. An example of using this would be when you want to get the size in memory of an array (which is the only thing I can think of that would be useful for this name).

Underscore.js unfortunately defines a size method which actually returns the length of an object or array. Since unfortunately the length property of a function is defined as the number of named arguments the function declares they had to use an alternative and size was chosen (count would have been a better choice).

.size() is not a native JS function of Array (at least not in any browser that I know of).

.length should be used.

If

.size() does work on your page, make sure you do not have any extra libraries included like prototype that is mucking with the Array prototype.

or

There might be some plugin on your browser that is mucking with the Array prototype.

The .size() function is available in Jquery and many other libraries.

The .length property works only when the index is an integer.

The length property will work with this type of array:

var nums = new Array();
nums[0] = 1; 
nums[1] = 2;
print(nums.length); // displays 2

The length property won't work with this type of array:

var pbook = new Array(); 
pbook["David"] = 1; 
pbook["Jennifer"] = 2;
print(pbook.length); // displays 0

So in your case you should be using the .length property.

.size() is jQuery's, much probably you're either confusing with or took from someone else who had imported the jQuery library to his project.

If you'd have jQuery imported and you'd write like $(array).size(), it would return the array length.

array.length isn't necessarily the number of items in the array:

var a = ['car1', 'car2', 'car3'];
a[100] = 'car100';
a.length; // 101

The length of the array is one more than the highest index.

As stated before Array.size() is not a valid method.

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