What is the javascript then method?

javascript then method is executed asynchronously, that is, the internal program of [then()] is executed after the method before [.then()] is executed. This avoids problems such as data not being obtained. The syntax is [promise.then(onCompleted, onRejected)].

The operating environment of this tutorial: Windows 7 system, JavaScript version 1.8.5, DELL G3 computer.

Thethen() method is executed asynchronously.

means: when the method before .then() is executed, the program inside then() will be executed. This will avoid problems such as data not being obtained.

Grammar:

promise.then(onCompleted, onRejected);

4. Parameters

• promise is required. Promise object.

• onCompletedRequired. The fulfillment handler function to run when the promise completes successfully.

• onRejectedOptional. Error handler function to run when the promise is rejected.

Example:

vstart() {
        super.start();
        if (this.transport) {
            return this.transport.ready.then(() => {
                return this.clientSM.start();
            });
        } else {
            return Promise.reject("no transport attached");
        }
    }

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