math.max in webgl

[webgllearn]

hi, 

I want to know what is how i can type this javascript code in webgl

maxrgb = Math.max(Math.max(r, g), b); 

when i use above javascript code in webgl script, it not works 

 i try float maxrgb = Math.max(Math.max(r, g), b);   

but it also not works 

So how to write above code in webgl ?

please help.!