Is JavaScript a memory safe language?
None of those are suitable options for an image decoding library on the range of WebP supported platforms.
What makes these unusable for this task?
No. That is true for the list upthread (well, if you consider runtimes measuring a couple of MB "large", it's reasonable but quite arguable). It doesn't have much correlation with any feature.
What makes them unsuitabe is lack of widespread compiler support across those platforms, if we ignore how long Ada has been available in GCC.
And Modula-2 is now in GCC as well.
Well Rust also has unsafe, better not use it.