We are also seeing performance issues with .splice. Visit https://user.sitepen.com/~nroberts/gfx.html, click “Create Circles” then click “Remove & Add Circles”.

This performance impact can be negated simply by performing a .splice call with a third argument (an object to be inserted into the array). Once this is done, normal .splice use may be resumed without performance issues.

You may see this speed improvement in effect by visiting the same page with a flag set (https://user.sitepen.com/~nroberts/gfx.html?fixSplice). We had to do a very specific sequence of operations in this exact order to restore the speed of a .splice operation:

* Do a normal .splice (view https://user.sitepen.com/~nroberts/gfx.html?fixSplice&skipStep=splice to see what happens when this is not true)
* Call .push (view https://user.sitepen.com/~nroberts/gfx.html?fixSplice&skipStep=push to see what happens when this is not true)
* Perform a no-op .splice where we insert a single object while removing a single object (view https://user.sitepen.com/~nroberts/gfx.html?fixSplice&skipStep=noop to see what happens when this is not true)

In addition, manually downshifting elements in the array to remove an item results in a speed improvement even beyond splice: https://user.sitepen.com/~nroberts/gfx.html?customSplice

Finally, if you visit the page as normal (https://user.sitepen.com/~nroberts/gfx.html) click “Create Circles” then click “Remove & Add Circles” then, in the console, set the global `recreateChildren = true` then click “Remove & Add Circles” again, this will recreate the internal array and also results in a speed improvement.

cbruni@ please take a look (might have been resolved by now).

https://user.sitepen.com/~nroberts/gfx.html?fixSplice:
    Elapsed time: 6778.52 splicing: 6449.98
    gfx.js:93 [ removeAndAddCircles ]: Num shapes =  4000

https://user.sitepen.com/~nroberts/gfx.html:
    Elapsed time: 6743.22 splicing: 6394.22
    gfx.js:93 [ removeAndAddCircles ]: Num shapes =  4000

https://user.sitepen.com/~nroberts/gfx.html: (recreateChildren = true)
    gfx.js:32 Elapsed time: 589.78 splicing: 260.77
    gfx.js:93 [ removeAndAddCircles ]: Num shapes =  4000

At least on the demo page that seems to be working now.


a = new Array(10000000); console.time(); a.splice(0, a.length); console.timeEnd()

However is still rather slow 165ms.

Wait, that seems to be only the case on the gfx website, so this is fine then:

a = new Array(10000000); console.time(); a.splice(0, a.length); console.timeEnd();
default: 0.02001953125ms

And even when setting elements on the Array.prototype:
Array.prototype[10] = 123;
a = new Array(10000000); console.time(); a.splice(0, a.length); console.timeEnd()
VM309:1 default: 82.975830078125ms

So this must have been fixed in the mean time (tested on M62).