CODEWITHSUNDEEP
javascriptnode.jspromiseecmascript-6
Reza Afzalan
Reza Afzalan

Reputation: 5756

How to check this promise state, when programming a new promise? js

I am programming a new promise, it has many different conditions that call reject() or resolve() related to their state, also I know that the promise state will set with the first call to reject() | resolve(). My question is: Is there any native (build-in) way to get the promise state? The following is a demonstrative-code:

exports.addStatement = function (db, description, data) {
    return new Promise(function (resolve, reject) {
        validator.validateStatement(description, data)
        .then(function (data) {
            //......
            if(cnd1)
               resolve(res);
            if(cnd2)
               reject(err);
            //......
            //How to check if this promise is rejected or resolved yet? 

        })
        .catch(function (err) {
            reject(err);
        })
    })
};

Upvotes: 2

Views: 7576

Answers (1)

jfriend00
jfriend00

Reputation: 707926

You cannot directly examine the state of a promise. That's not how they work. You can use .then() or .catch() on them with a callback to get notified.

Or, in your specific case, you can probably change the way your code is structured to remove the anti-pattern of creating an unnecessary outer promise and switching your logic to if/else if/else.

Here's the cleaned up code:

exports.addStatement = function (db, description, data) {
    return validator.validateStatement(description, data)
        .then(function (data) {
            //......
            if(cnd1) {
               // make res be the resolved value of the promise
               return res;
            } else if(cnd2) {
               // make promise become rejected with err as the reason
               throw err;
            } else {
               // decide what else to do here
            }
        })
    })
};

If you couldn't make an if/else work for you, the above structure should still work because both the return and the throw terminate the execution of the .then() handler. So, the only code that continues after them is code that has not yet set the resolved/rejected value for the current promise so you don't have to look at the state of the promise to know that. If the code gets past the return and throw and is still executing, then neither of those was executed and the resolved/rejected value of the current promise is still unset.

Upvotes: 4

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