How to send whatsapp message in whatsapp-web.js

I am using whatsapp-web.js to send and reply message. https://github.com/pedroslopez/whatsapp-web.js

I can connect and reply message using following code:

const { Client } = require('whatsapp-web.js');
const client = new Client();

client.on('qr', (qr) => {
    // Generate and scan this code with your phone
    console.log('QR RECEIVED', qr);
});

client.on('ready', () => {
    console.log('Client is ready!');
});

client.on('message', msg => {
    if (msg.body == '!ping') {
        msg.reply('pong');
    }
});

client.initialize();

how can I send new message in whatsapp to mobile number??

Here is how I send messages in whatsapp-web.js.

const number = "9830121234";
const sanitized_number = number.toString().replace(/[- )(]/g, ""); // remove unnecessary chars from the number
const final_number = `91${sanitized_number.substring(sanitized_number.length - 10)}`; // add 91 before the number here 91 is country code of India

const number_details = await client.getNumberId(final_number); // get mobile number details

if (number_details) {
    const sendMessageData = await client.sendMessage(number_details._serialized, sendData.message); // send message
} else {
    console.log(final_number, "Mobile number is not registered");
}

.

.

update (for await is valid inside only async error):

if you are using this method in any event you should put it inside an async function

on.any_kind_of_event(async function () {
    const number = "9830121234";
    const sanitized_number = number.toString().replace(/[- )(]/g, ""); // remove unnecessary chars from the number
    const final_number = `91${sanitized_number.substring(sanitized_number.length - 10)}`; // add 91 before the number here 91 is country code of India

    const number_details = await client.getNumberId(final_number); // get mobile number details

    if (number_details) {
        const sendMessageData = await client.sendMessage(number_details._serialized, sendData.message); // send message
    } else {
        console.log(final_number, "Mobile number is not registered");
    }
});