Digits separator is pronounced when the tens digit is missing

[waelhasan]

When the given number has zero value in the tens digit, the separator (which separates the digit in the same unit) is concatenated to the correct pronunciation of the number

Note that his bug only works in Arabic

Examples

console.log(convert(870)) // ثمان مئة و  وسبعون
console.log(convert(70)) // و سبعون

console.log(convert(870, { separator: 'ثم' })) // logs: "ثمان مئة ثم  ثمسبعون"
console.log(convert(70, { separator: 'ثم' })) // logs: " ثم سبعون"