Ново обещание, решителност
Примерен код
оставете срещу обещания за връщане на js
In simple terms, inside a then handler function:
A) When x is a value (number, string, etc):
- return x is equivalent to return Promise.resolve(x)
- throw x is equivalent to return Promise.reject(x)
B) When x is a Promise that is already settled (not
pending anymore):
- return x is equivalent to return Promise.resolve(x),
if the Promise was already resolved.
- return x is equivalent to return Promise.reject(x),
if the Promise was already rejected.
C) When x is a Promise that is pending:
- return x will return a pending Promise, and it will
be evaluated on the subsequent then.
Read more on this topic on the Promise.prototype.then() docs.Обещавам.d
var original = Promise.resolve(33);
original.then( val => console.log('origianl', val);
var cast = Promise.resolve(original);
cast.then(function(value) {
console.log('value: ' + value);
});
console.log('original === cast ? ' + (original === cast));
// logs, in order:
// original === cast ? true
// value: 33
обещание за разрешаване отхвърли
function testFunction(value) {
return new Promise(function (resoleve, reject) {
setTimeout(function () {
let n = value;
if (n < 100) {
resoleve("範囲内");
} else {
reject("範囲外");
}
}, 2000);
})
}
testFunction(10)
.then(function (value) {
console.log(value);
return testFunction(50);
})
.then(function (value) {
console.log(value);
return testFunction(150);
})
.catch(function (error) {
console.log(`エラーです。${error}`);
})
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