Compatibility

Consistent type coercion when modifying variables

In Scratch 2.0 if you set [var] to [var + 1] and the variable contains a string, you get 1. If you change [var] by [1] when the variable contains a string, you get NaN. In 3.0 both now have the same behavior and return 1.

Consistent rounding method for list indexes

In Scratch 2.0 if you delete [1.5] of [list] it will delete the item at index 2 as the index is rounded. However if you replace item [1.5] of [list] with ["thing"] it will replace the item at index 1 as floor is applied to the index. In 3.0 floor is now applied consistently for all index arguments on list blocks.

Reference: https://github.com/LLK/scratch-vm/issues/202

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Proposed: Consistent direction for "whirl" graphic effect

Scratch 2.0 has two stage modes: 2D and 3D. The "whirl" graphic effect is applied inconsistently between these two modes (clockwise in 2D and counter-clockwise in 3D). Because most users see the 3D stage when using Scratch 2.0 and Scratch 3.0 always uses WebGL for rendering, we have decided to normalize to counter-clockwise application of the "whirl" effect.

Reference: https://github.com/LLK/scratch-render/issues/22