Q:

Javascript: Split a string into array matching parameters

I have a string that has numbers and math operators (+,x,-, /) mixed in it
'12+345x6/789'
I need to convert it into an array seperated by those math operators.
[12, +, 345, x, 6, /, 789]
What is a simple way of doing this? 

A:

Splitting on consecutive non-digit chars \D+ you get

console.log ('12+345x6/789'.split (/\D+/))
// [ '12', '345', '6', '789' ]

If you add a capture group, (\D+) you get the separator too

console.log ('12+345x6/789'.split (/(\D+)/))
// [ "12", "+", "345", "x", "6", "/", "789" ]

If you want to support parsing decimals, change the regexp to /([^0-9.]+)/ - Note, \D used above is equivalent to [^0-9], so all we're doing here is adding . to the character class

console.log ('12+3.4x5'.split (/([^0-9.]+)/))
// [ "12", "+", "3.4", "x", "5" ]

And a possible way to write the rest of your program

const cont = x =>
  k => k (x)

const infix = f => x =>
  cont (f (x))

const apply = x => f =>
  cont (f (x))

const identity = x =>
  x

const empty =
  Symbol ()
  
const evaluate = ([ token = empty, ...rest], then = cont (identity)) => {
  if (token === empty) {
    return then
  }
  else {
    switch (token) {
      case "+":
        return evaluate (rest, then (infix (x => y => x + y)))
      case "x":
        return evaluate (rest, then (infix (x => y => x * y)))
      case "/":
        return evaluate (rest, then (infix (x => y => x / y >> 0)))
      default:
        return evaluate (rest, then (apply (Number (token))))
    }
  }
}

const parse = program =>
  program.split (/(\D+)/)
  
const exec = program =>
  evaluate (parse (program)) (console.log)

exec ('')             // 0
exec ('1')            // 1
exec ('1+2')          // 3
exec ('1+2+3')        // 6
exec ('1+2+3x4')      // 24
exec ('1+2+3x4/2')    // 12
exec ('12+345x6/789') // 2

