read evaluate print loop of grease monkey environment

grease-monkey-repl.user.js

// ==UserScript==
// @name  greasy monkey repl
// @description  read evaluate print loop of grease monkey environment
// @namespace  http://gholk.github.io/
// @version  4
// @match  *
// @grant  GM.info 
// @grant  GM.deleteValue 
// @grant  GM.getValue 
// @grant  GM.listValues 
// @grant  GM.setValue 
// @grant  GM.getResourceUrl 
// @grant  GM.notification 
// @grant  GM.openInTab 
// @grant  GM.setClipboard 
// @grant  GM.xmlHttpRequest 
// @grant  unsafeWindow 
// ==/UserScript==

async function repl() {
    let result = 'input javascript code'
    while (true) {
        const expression = prompt(result)
        result = await eval(expression)
        await sleep(0)
    }
}

function xmlHttpRequestPromise(url, option) {
    return new Promise(resolve => {
        const newOption = {url, onload, ...option}
        if (!newOption.method) newOption.method = 'GET'
        GM.xmlHttpRequest(newOption)
        function onload(response) {
            resolve(response)
        }
    })
}

function sleep(second) {
    return new Promise(wake => setTimeout(wake, second * 1000))
}

repl()