Difference between Array.length = 0 and Array =[]?
foo = []
creates a new array and assigns a reference to it to a variable. Any other references are unaffected and still point to the original array.
foo.length = 0
modifies the array itself. If you access it via a different variable, then you still get the modified array.
Read somewhere that the second one creates a new array by destroying all references to the existing array
That is backwards. It creates a new array and doesn't destroy other references.
var foo = [1,2,3];
var bar = [1,2,3];
var foo2 = foo;
var bar2 = bar;
foo = [];
bar.length = 0;
console.log(foo, bar, foo2, bar2);
gives:
[] [] [1, 2, 3] []
arr.length =0;// expected to empty the array
and it does empty the array, at least the first time. After the first time you do this:
arr = arr + $(this).html();
… which overwrites the array with a string.
The length
property of a string is read-only, so assigning 0
to it has no effect.
The difference here is best demonstrated in the following example:
var arrayA = [1,2,3,4,5];
function clearUsingLength (ar) {
ar.length = 0;
}
function clearByOverwriting(ar) {
ar = [];
}
alert("Original Length: " + arrayA.length);
clearByOverwriting(arrayA);
alert("After Overwriting: " + arrayA.length);
clearUsingLength(arrayA);
alert("After Using Length: " + arrayA.length);
Of which a live demo can be seen here: http://www.jsfiddle.net/8Yn7e/
When you set a variable that points to an existing array to point to a new array, all you are doing is breaking the link the variable has to that original array.
When you use array.length = 0
(and other methods like array.splice(0, array.length)
for instance), you are actually emptying the original array.