如何从回调JavaScript导出结果

Question

How to export result from callback javascript to global variable

function capsule (a, b, callback) {
    var res = a + b
    callback( res )
}


capsule(5, 2, n => {
    var result = n
    // console.log(result)
})

// i need do operation with result here, outside the callback
console.log(result) // result is undefined
console.log("ok")

The console back result is undefined

Answer 1

result is only defined inside of your callback. If you define it outside, it will work.

function capsule (a, b, callback) {
    var res = a + b
    callback( res )
}

var result;
capsule(5, 2, n => {
    result = n
})

console.log(result)
console.log("ok")

Answer 2

 capsule(5, 2, n => { var result = n 

var declares a variable that is local to the function.

Declare it outside

var result;

capsule(5, 2, n => {
    result = n

---

It would probably make more sense to return the value rather than to use a callback though:

function capsule (a, b) {
    var res = a + b;
    return res;
}

var result = capsule(5, 2);
console.log(result);