Mod Studio Task

task.js

const inputString =
  '[ "AND", ["<", "var1", "var2"], [ "OR", [">", "var3", "var4"], ["==", "var5", "var6"] ] ]'

let cleanedString = ''
for (var i = 0; i < inputString.length; i++) {
  if (
    inputString[i] !== '[' &&
    inputString[i] !== ']' &&
    inputString[i] !== '"'
  ) {
    cleanedString += inputString[i]
  }
}

let arrayString = []
let tempString = '',
  j = 0
for (var i = 0; i < cleanedString.length; i++) {
  if (cleanedString[i] === ',' || i === cleanedString.length - 1) {
    arrayString[j] = tempString.trim()
    j++
    tempString = ''
  } else {
    tempString += cleanedString[i]
  }
}

let operStash = [],
  finalArray = []
for (var i = 0; i < arrayString.length; i++) {
  arrayString[i]
  if (
    arrayString[i] === 'AND' ||
    arrayString[i] === 'OR' ||
    arrayString[i] === '>' ||
    arrayString[i] === '<' ||
    arrayString[i] === '=='
  ) {
    operStash.push(arrayString[i])
  } else {
    finalArray.push(arrayString[i])
    if (operStash.length !== 0) {
      finalArray.push(operStash.pop())
    }
  }
}

let c = [],
  andOpened = false
for (var i = 0; i < finalArray.length; i++) {
  if (finalArray[i] === 'AND') {
    if (andOpened) {
      c.push(')')
      c.push('AND')
      c.push('(')
      andOpened = true
    } else {
      c.push('AND')
      c.push('(')
      andOpened = true
    }
  } else {
    c.push(finalArray[i])
    if (andOpened && i === finalArray.length - 1) {
      c.push(')')
    }
  }
}

const finalString = c.join(' ')
console.log(finalString)