Number to words (crore and lakh)

Number to words (Indian style - crore, lakh). The function is recursive.

const HUNDRED = 100;
const THOUSAND = HUNDRED * 10;
const LAKH = THOUSAND * 100;
const CRORE = LAKH * 100;

function number2words(num)
{
    let str = '';     

    if (num >= CRORE)
    {        
        str += number2words(Math.floor(num / CRORE)) + " crore";
        num %= CRORE;
    }

    if (num >= LAKH)
    {        
        str += number2words(Math.floor(num / LAKH)) + " lakh";
        num %= LAKH;
    }

    if (num >= THOUSAND)
    {        
        str += number2words(Math.floor(num / THOUSAND)) + " thousand";
        num %= THOUSAND;
    }

    if (num >= HUNDRED)
    {        
        str += number2words(Math.floor(num / HUNDRED)) + " hundred";
        num %= HUNDRED;
    }

    if (num >= 10)
    {
        let ty = ''; // Number words ending in ty like thirty and seventy
        let tn = ''; // Number words ending in the teens
        const tens_digit = Math.floor(num / 10);

        switch(tens_digit)
        {
            case 1:                
                switch (num)
                {
                    case 10: tn = " ten"; break;
                    case 11: tn = " eleven"; break;
                    case 12: tn = " twelve"; break;
                    case 13: tn = " thirteen"; break;
                    case 14: tn = " fourteen"; break;
                    case 15: tn = " fifteen"; break;
                    case 16: tn = " sixteen"; break;
                    case 17: tn = " seventeen"; break;
                    case 18: tn = " eighteen"; break;
                    case 19: tn = " nineteen"; break;
                }                
            break;
            case 2: ty = " twenty"; break;
            case 3: ty = " thirty"; break;
            case 4: ty = " forty"; break;
            case 5: ty = " fifty"; break;
            case 6: ty = " sixty"; break;
            case 7: ty = " seventy"; break;
            case 8: ty = " eighty"; break;
            case 9: ty = " ninety"; break;
        }

        if (tens_digit === 1)
        {
            str += tn;            
        }
        else
        {
            str += ty;
            num %= 10;
        }
    }

    if (num >= 1)
    {
        num = Math.floor(num / 1);

        switch (num)
        {
            case 1 : str += " one"; break;
            case 2 : str += " two"; break;
            case 3 : str += " three"; break;
            case 4 : str += " four"; break;
            case 5 : str += " five"; break;
            case 6 : str += " six"; break;
            case 7 : str += " seven"; break;
            case 8 : str += " eight"; break;
            case 9 : str += " nine"; break;
        }        
    }

    return str;
}

console.log(number2words(987654).trim());

refactored to using arrays

const HUNDRED = 100;
const THOUSAND = HUNDRED * 10;
const LAKH = THOUSAND * 100;
const CRORE = LAKH * 100;

const TN = ['ten', 'eleven', 'twelve', 'thirteen', 'fourteen', 'fifteen', 'sixteen', 'seventeen', 'eighteen', 'nineteen'];
const TY = ['twenty', 'thirty', 'forty', 'fifty', 'sixty', 'seventy', 'eighty', 'ninety'];
const O = ['one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine'];

function number2words(num)
{
    let str = '';     

    if (num >= CRORE)
    {        
        str += number2words(Math.floor(num / CRORE)) + " crore";
        num %= CRORE;
    }

    if (num >= LAKH)
    {        
        str += number2words(Math.floor(num / LAKH)) + " lakh";
        num %= LAKH;
    }

    if (num >= THOUSAND)
    {        
        str += number2words(Math.floor(num / THOUSAND)) + " thousand";
        num %= THOUSAND;
    }

    if (num >= HUNDRED)
    {        
        str += number2words(Math.floor(num / HUNDRED)) + " hundred";
        num %= HUNDRED;
    }

    if (num >= 10)
    {
        const tens_digit = Math.floor(num / 10);

        if (tens_digit === 1)
        {            
            str += ' ' + TN[num - 10];
            num = 0; // This is to prevent for example : 12 to trickle down as 12%10 = 2
        }
        else
        {
            str += ' ' + TY[tens_digit - 2];
            num %= 10;
        }
    }

    if (num >= 1)
    {
        num = Math.floor(num / 1);
        str += ' ' + O[num - 1];
    }

    return str;
}

console.log(number2words(987654).trim());

node number2words.js 
nine lakh eighty seven thousand six hundred fifty four