Javascript promise, async function and await

How to use async functionality in Javascript?

An async function returns a promise. If this promise has done, the await function will be execute. A await function can only exists in async function.

Aysnc loading Example in Javascript:

function loadHeader() {
    return getAllContent().then(function(content) {
        return content[0].header;
    }).catch(function(err) {
        return {
          content: 'loading error'
        };
	});
}

async function getHeader() {
    try {
        let content = await getAllContent();
        return content[0].header;
    } catch (err) {
        return {
            content: 'loading error'
        };
    }
}