javascript supports unicode.
Proof:
゚ω゚ノ=/`m´)ノ~┻━┻//*´∇`*/['_'];o=(゚ー゚)=_=3;c=(゚Θ゚)=(゚ー゚)-(゚ー゚);(゚Д゚)=(゚Θ゚)=(o^_^o)/(o^_^o);(゚Д゚)={゚Θ゚:'_',゚ω゚ノ:((゚ω゚ノ==3)+'_')[゚Θ゚],゚ー゚ノ:(゚ω゚ノ+'_')[o^_^o-(゚Θ゚)],゚Д゚ノ:((゚ー゚==3)+'_')[゚ー゚]};(゚Д゚)[゚Θ゚]=((゚ω゚ノ==3)+'_')[c^_^o];(゚Д゚)['c']=((゚Д゚)+'_')[(゚ー゚)+(゚ー゚)-(゚Θ゚)];(゚Д゚)['o']=((゚Д゚)+'_')[゚Θ゚];(゚o゚)=(゚Д゚)['c']+(゚Д゚)['o']+(゚ω゚ノ+'_')[゚Θ゚]+((゚ω゚ノ==3)+'_')[゚ー゚]+((゚Д゚)+'_')[(゚ー゚)+(゚ー゚)]+((゚ー゚==3)+'_')[゚Θ゚]+((゚ー゚==3)+'_')[(゚ー゚)-(゚Θ゚)]+(゚Д゚)['c']+((゚Д゚)+'_')[(゚ー゚)+(゚ー゚)]+(゚Д゚)['o']+((゚ー゚==3)+'_')[゚Θ゚];(゚Д゚)['_']=(o^_^o)[゚o゚][゚o゚];(゚ε゚)=((゚ー゚==3)+'_')[゚Θ゚]+(゚Д゚).゚Д゚ノ+((゚Д゚)+'_')[(゚ー゚)+(゚ー゚)]+((゚ー゚==3)+'_')[o^_^o-゚Θ゚]+((゚ー゚==3)+'_')[゚Θ゚]+(゚ω゚ノ+'_')[゚Θ゚];(゚ー゚)+=(゚Θ゚);(゚Д゚)[゚ε゚]='\\';(゚Д゚).゚Θ゚ノ=(゚Д゚+゚ー゚)[o^_^o-(゚Θ゚)];(o゚ー゚o)=(゚ω゚ノ+'_')[c^_^o];(゚Д゚)[゚o゚]='\"';(゚Д゚)['_']((゚Д゚)['_'](゚ε゚+(゚Д゚)[゚o゚]+(゚Д゚)[゚ε゚]+(゚Θ゚)+(゚ー゚)+(゚Θ゚)+(゚Д゚)[゚ε゚]+(゚Θ゚)+((゚ー゚)+(゚Θ゚))+(゚ー゚)+(゚Д゚)[゚ε゚]+(゚Θ゚)+(゚ー゚)+((゚ー゚)+(゚Θ゚))+(゚Д゚)[゚ε゚]+(゚Θ゚)+((o^_^o)+(o^_^o))+((o^_^o)-(゚Θ゚))+(゚Д゚)[゚ε゚]+(゚Θ゚)+((o^_^o)+(o^_^o))+(゚ー゚)+(゚Д゚)[゚ε゚]+((゚ー゚)+(゚Θ゚))+(c^_^o)+(゚Д゚)[゚ε゚]+(゚ー゚)+((o^_^o)-(゚Θ゚))+(゚Д゚)[゚ε゚]+(゚Θ゚)+(゚Θ゚)+(c^_^o)+(゚Д゚)[゚ε゚]+(゚Θ゚)+(゚ー゚)+((゚ー゚)+(゚Θ゚))+(゚Д゚)[゚ε゚]+(゚Θ゚)+((゚ー゚)+(゚Θ゚))+(゚ー゚)+(゚Д゚)[゚ε゚]+(゚Θ゚)+((゚ー゚)+(゚Θ゚))+(゚ー゚)+(゚Д゚)[゚ε゚]+(゚Θ゚)+((゚ー゚)+(゚Θ゚))+((゚ー゚)+(o^_^o))+(゚Д゚)[゚ε゚]+(゚ー゚)+(c^_^o)+(゚Д゚)[゚ε゚]+(゚Θ゚)+((o^_^o)-(゚Θ゚))+((゚ー゚)+(o^_^o))+(゚Д゚)[゚ε゚]+(゚Θ゚)+((゚ー゚)+(゚Θ゚))+((゚ー゚)+(o^_^o))+(゚Д゚)[゚ε゚]+(゚Θ゚)+((o^_^o)+(o^_^o))+((o^_^o)-(゚Θ゚))+(゚Д゚)[゚ε゚]+(゚Θ゚)+((゚ー゚)+(゚Θ゚))+(゚ー゚)+(゚Д゚)[゚ε゚]+(゚Θ゚)+(゚ー゚)+(゚ー゚)+(゚Д゚)[゚ε゚]+(゚ー゚)+((o^_^o)-(゚Θ゚))+(゚Д゚)[゚ε゚]+((゚ー゚)+(゚Θ゚))+(゚Θ゚)+(゚Д゚)[゚o゚])(゚Θ゚))('_');
The above code prooves that js indeed supports unicode. The above code alerts "Hello World" and is taken from here
So, it is not js' fault. Fault is somewhere else, or the system is unable to show those characters.