About JavaScript asynchronous calling methods

Question

You can modify the following aa() function, the purpose is to use console.log() to output the want-value after one second

function aa() {
    setTimeout(function() {
        return "want-value";
    }, 1000);
}

However, there are additional requirements:

1. ##aa() The function can be modified at will, but there cannot be a console. log()

2. Execution

   console.log() There cannot be a setTimeout package in the statement

##setTimeout()

function aa(callback) {
    setTimeout(function() {
        if (typeof callback === "function") {
            callback("want-value");
        }
    }, 1000);
}

aa(function(v) {
    console.log(v);
});

function aa() {
    return new Promise(resolve => {
        setTimeout(function() {
            resolve("want-value");
        }, 1000);
    });
}

aa().then(v => console.log(v));

function aa() {
    return new Promise(resolve => {
        setTimeout(function() {
            resolve("want-value");
        }, 1000);
    });
}

async function main() {
    const v = await aa();
    console.log(v);
}

main();

aa()

await is used to wait asynchronously. After waiting for the asynchronous result, use console.log() to process it. It should be noted here that await

async method, so in order to use await you must define an async's main method and called in the global scope. Since the main method is asynchronous (declared as async), if there are other statements after main() is called, such as console.log("hello"), then this sentence will be executed first. async/await syntax makes writing asynchronous calls like writing synchronous code. When writing code, you can avoid logical jumps and write it more easily. (Reference: From hell to heaven, Node callback changes to async/await)

main()

main() You can use IIFE for this part Encapsulate it,

(async () => {
    const v = await aa();
    console.log(v);
})();

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