I want to know what is the difference between using async function and function only. Of course, with asynchronous functions you can use await and they return a Promise .
But is there any other effect? Is there any difference in the way the code runs?
When a normal function is executed, it runs sequentially . That is, if you have two functions A () and B () and execute them in that order, the B () function will only be called when the A () function finishes its execution.
By contrast, if you have an asynchronous function A () (for example, that performs an I / O operation or other blocking operation), it can be called and while the operation is performed you can execute another function B () ( asynchronous or not) in the main context. Later, the A () function will return its value when the operation is finished and the main thread is available for that.
Warning that synchronous / asynchronous does not have to do with multi-threading.
You write "linearly" rather than with so many callbacks ... Example:
function resolveDepoisDe2Segundos() {
return new Promise(resolve => {
setTimeout(() => {
resolve('resolvido');
}, 2000);
});
}
async function teste() {
console.log('inicio');
var resultadoAwait = await resolveDepoisDe2Segundos();
var resultadoPromisse = resolveDepoisDe2Segundos();
console.log('resultado await', resultadoAwait);
console.log('resultado promisse then', resultadoPromisse.then(function(resultado){
console.log('resultado promisse resolved', resultado);
}));
console.log('fim');
}
teste();