Learning await/async in Javascript

learn-async-await.js

async function start () {
    try {
        let result1 = await callAwaitFunction(2);
        console.log(result1);

        let result2 = await callAwaitFunction(-1);
        console.log(result2);

        // these 2 lines won't be reached because of the exception
        let result3 = await callAwaitFunction(2);
        console.log(result3);

    } catch (e) {
        console.log('err: ', e);
    }
}

async function callAwaitFunction(number) {
    console.log('call callAwaitFunction('+ number +')');
    return new Promise(function(resolve, reject) {
        setTimeout(function() {
            if (number >= 0) {
                resolve('It\'s a positive.')
            } else {
                reject('It\'s a negative.')
            }
        }, 1000)
    })
}

// notice that we can't use await in a regular function or top level code,
// so we need to have a wrapping async function
start();

output

call callAwaitFunction(2)
It's a positive.
call callAwaitFunction(-1)
err:  It's a negative.