NodeJS await/async not working in object

Question

I'm currently working on a validation module in nodeJs and I cannot seem to understand how or why does the async/await does not work in my current module.

In the module I should be able to have more than one validation exports ex: Forms, Data etc.

Each object should have more that one validation functions, ex: forms should have register, login, add etc...

This is my approach

var forms = {
    validation: {
        status: true,
        data: {},
        error: {}
    },

    register: async(data) => new Promise((resolve, reject) => {
        var validation = forms.validation;

        try {
            const errorMessages = await forms.getErrorMessages('register');
            ...
        } catch (error) {
            reject(error);
        }
    }),


    getErrorMessages: (key) => new Promise((resolve, reject) => {
        Errors.
        findOne({ type: 'validation', 'identifier': key }).
        select('content').
        populate('content'). // only works if we pushed refs to children
        exec(function(err, contentObj) {
            if (err) reject(err);
            var errorMessages = {};
            const contentArray = contentObj.content;
            for (var i = 0; i < contentArray.length; i++) {
                var key = contentArray[i].identifier,
                    message = contentArray[i].message;
                errorMessages[key] = message;
            }
            resolve(errorMessages);
        });
    }),

};
exports.forms = forms;

Now at the register function, which is defined as async function, in try I have that await forms.getErrorMessages('register') which should return the validation error messages from the database... The function works, it's defined to return a promise but I always get SyntaxError: Unexpected identifier for the function...

Can anyone explain why this doesn't work?

Thanks

The SyntaxError you're seeing should include additional info like a line-number. Can you mark the line in your code and add the full exception, too? — Lukas Knuth
– Lukas Knuth, Commented Mar 2, 2018 at 9:13
/home/sabin/Work/purchase/napi/api/services/validationService.js:74 const errorMessages = await forms.getErrorMessages('register'); SyntaxError: Unexpected identifier The unexpected identifier is marked at 'forms' — Sabbin
– Sabbin, Commented Mar 2, 2018 at 9:14
When in an async function you don't need to create a new promise unless you are resolving a callback. Mongoose can return promises as well, so you don't need to use it's callback interface either — Matt
– Matt, Commented Mar 2, 2018 at 9:25

Matt · Accepted Answer · 2018-03-02 09:44:37Z

2

There's no need to create new Promises when you already have a Promise. That is only required when you are converting some API that is not a promise into a promise.

Mongoose can return promises natively too, and the async function will allow any errors that are thrown to bubble up through the promises.

var forms = {

    validation: {
        status: true,
        data: {},
        error: {}
    },

    register: async (data) => {
        var validation = this.validation;
        const errorMessages = await this.getErrorMessages('register');
        ...
    },


    getErrorMessages: async (key) => {
        let contentObj = await Errors.findOne({ type: 'validation', 'identifier': key })
            .select('content')
            .populate('content') // only works if we pushed refs to children
            .exec()

        let errorMessages = {};
        const contentArray = contentObj.content;
        for (var i = 0; i < contentArray.length; i++) {
             let key = contentArray[i].identifier;
             let message = contentArray[i].message;
             errorMessages[key] = message;
        }
        return errorMessages;

    }

};
exports.forms = forms;

edited Mar 2, 2018 at 9:44

answered Mar 2, 2018 at 9:37

Matt

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4 Comments

Sabbin Over a year ago

Thanks! This worked, it will take a time to understand where the promise should be put and where not...

Matt Over a year ago

Whenever you use async you get a new promise, it's not exactly like new Promise as you can't resolve values or reject errors but you can return values and throw errors.

Matt Over a year ago

You might still need new Promise when you are converting a stream or callback into a promise, but it's getting rarer

Sabbin Over a year ago

Thanks for the info

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