Clear javascript arrays? Isn't it a = []? Indeed, this will make a an empty array. However, when a is referenced by other functions or objects, things become more complicated.
For instance, we have code below
var a = [1, 2, 3];
var obj = {
b: a
};
// clear array
a = [];
// oops! obj.b is not updated with a
console.assert(obj.b.length === 0);
In code above, we created an array a, and an object with a property b, which is referencing array a. Then we tried to clear array a by assigning it to an empty array. Since obj.b is referencing to a, we expect that it is also cleared. But the result is that obj.b still keeps the old value of a. So, what's happenning here?
As you might have guessed, the reason is that a is just a reference! When we are creating obj, obj.b is actually referring to the object that a is referencing, not a itself. So, when we assign a new empty array to a, obj.b is not affected at all, it is still referring to the old object.
Since there are no clear method in array object, what is the right way to clear it?
One way is to perform pop operations until the array is empty. The reason why pop works is that it is modifying the object in place, not creating a new object.
var a = [1, 2, 3];
var obj = {
b: a
};
// pop element until array is empty
while (a.length) {
a.pop();
}
console.assert(obj.b.length === 0);
But it may seems a little awkward to do such a simple operation. Here is a tricky way to get the job done.
var a = [1, 2, 3];
var obj = {
b: a
};
a.length = 0;
console.assert(obj.b.length === 0);
In code above, we are taking advantage of array.length property, when it is assigned to a length that is shorter than the real length, the array is truncated. So a.length = 0 will truncate all the elements in array.
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