I've picked up CodeSignal again and aim to solve something every day (either challenges or casual problems). Recently, we got a medium challenge from hamlet_m1. It is to emulate a CPU assembly language. (Hope I didn't mix up technical terms).

This time, I'm proud to be one of the JS solvers together with other 8 geeks:

The best solution by thomasz is an awe to me! Not only is it far shorter than all other solutions, but it is also still highly readable (to people like me who like hacky tricks)

Disclaimer: the full solution just for reference, please tell me to delete it if I violated any rule...

cpuEmulator = s => {

    z = 2 ** 32
    r = Array( 43 ).fill( 0 )
    R = x => +x.split`R`[ 1 ]

    for ( d = 0; l = s[ d++ ]; ) {

        [ c, a, b ] = l.split(/[\s,]/)
        o = y => r[ R( a ) ] = ( r[ R( a ) ] + y + z ) % z

        c == 'MOV' ?
            r[ R( b ) ] = R( a ) + 1 ? r[ R( a ) ] : +a  :            
        c == 'ADD' ?
            o( r[ R( b ) ] ) :
        c == 'DEC' ?
            o( -1 ) :
        c == 'INC' ?
            o( 1 ) :
        c == 'INV' ?
            o( ~r[ R( a ) ] * 2 + 1 ) :
        c == 'JMP' || c == 'JZ' && !r[ 0 ] ?
            d = +a - 1 : 0       
    }

    return r[ 42 ] + ''
}

Here are some tricks I discovered in this snippet:

1. Array(n).fill(x) to initialize an array of length n with prefilled values x (be careful about multi-dimension arrays though)
2. +'numeric string' to cast a string as a number or NaN
3. Regex /[xyz]/ to split string by separators x, y, z simultaneously
4. c == 'case1' ? ... : c == 'case2' ? ... : ... to well format nested ternary operators as a switch-case
5. number + '' to cast a number as a string

Feel free to drop a comment about your takeaways :D