gqlPing.js

function gqlPing(server, delay = 0) {
    return new Promise((res, rej) => {
        const ws = new WebSocket(`ws://${server}`, 'graphql-ws')
        let timeoutId = undefined
        let lastTime = undefined;
        const doPing = () => {
            ws.send(`{"id":"1","type":"start","payload":{"variables":{},"extensions":{},"operationName":null,"query":"subscription{serverInfo{online}}"}}`)
            lastTime = Date.now()
        }
        ws.onmessage = (e) => {
            const data = JSON.parse(e.data)
            if (data.type === 'data' && data.id === '1') {
                let delta = Date.now() - lastTime
                res(delta)
                ws.send(`{"id":"1","type":"stop"}`)
                ws.close()
            }
        }
        ws.onclose = () => {
            timeoutId && clearTimeout(timeoutId)
        }
        ws.onerror = (e) => {
            rej(e)
        }
        ws.onopen = () => {
            ws.send(`{"type":"connection_init","payload":{}}`)
            timeoutId = setTimeout(doPing, delay)
        }
    })
}

// example: gqlPing('localhost:11451').then((ms) => console.log(ms))