Right syntax for extrapolating a variable with javascript template literals?

Question

Could somebody please point me in the right direction regarding the correct syntax of template literals ?

I have the following code (without template literals, works just fine) :

const dbUrl = 'localhost:27017/imgManager';
mongoose.connect('mongodb://' + dbUrl, { useNewUrlParser: true });

Now I'd like to put useNewUrlParser: true in a variable :

const dbUrl = 'localhost:27017/imgManager',
      dbOptions = 'useNewUrlParser: true';
mongoose.connect('mongodb://' + dbUrl, { dbOptions });

Doesn't work of course, mongoose.connect() complains it has no dbOptions :

$ node server.js 
Server up: http://localhost:3300
the options [dbOptions] is not supported

I guess template literals are the way to go, but what's the right syntax ? I tried the following, but none works :

`mongoose.connect('mongodb://' + dbUrl, { ${dbOptions} });`
mongoose.connect(`mongodb://${dbUrl}, { ${dbOptions} }`);
mongoose.connect(`mongodb:\/\/${dbUrl}, { ${dbOptions} }`);

Any idea ?

Why do you want to have all the parameters as a *single string* and somehow expect the method to read that string and interpret what the parameters are? — VLAZ, Mar 10 '19 at 12:57
The more I look at this, the more I think it's an [XY problem](https://meta.stackexchange.com/questions/66377/what-is-the-xy-problem) - I don't think your query has anything to do with template literals, nor is the solution to use them. If you want to store the `dbOptions` as a variable, you'd do `dbOptions = { useNewUrlParser: true }` and then call `mongoose.connect('mongodb://' + dbUrl, dbOptions);` — VLAZ, Mar 10 '19 at 13:00

score 1 · Answer 1 · answered Mar 10 '19 at 13:00

Template literals don't work in arbitrary position, and they don't create arbitrary JS syntax. (Without a tag) they create strings only, and only a single value never two arguments at once. As options, you need to pass an object:

const dbUrl = 'localhost:27017/imgManager',
      dbOptions = { useNewUrlParser: true };
mongoose.connect(
   `mongodb://${ dbUrl }`, // first argument
    dbOptions // second argument
);

If you really get the options as a string, you would need to parse them into an object, e.g.:

const dbUrl = 'localhost:27017/imgManager',
      dbOptions = '"useNewUrlParser": true';
mongoose.connect(
   `mongodb://${ dbUrl }`, // first argument
    JSON.parse(`{${ dbOptions }}`) // second argument. The string is '{' + dbOptions + '}'
);

score 1 · Accepted Answer · answered Mar 10 '19 at 13:01

1

Template literals are only for strings, not objects. dbOptions should be an object, not a string.

const dbOptions = { useNewUrlParser: true };

Then you use the variable itself:

mongoose.connect('mongodb://' + dbUrl, dbOptions);

answered Mar 10 '19 at 13:01

Barmar

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Thanks ! Works fine ! – ChennyStar Mar 10 '19 at 13:32

Ele · Answer 3 · 2019-03-10T13:13:48.903

0

As dbOptions is a string in your approach, this { dbOptions } is creating a js object as follow:

// cause that mongoose is complaining because it's not expecting 
// options with property name dbOptions
{ dbOptions: 'useNewUrlParser: true' }

You should do the following

const dbUrl = 'localhost:27017/imgManager',
      dbOptions = {useNewUrlParser: 'true'};    

// `mongodb://${dbUrl}` will generate the following string:
//  "mongodb://localhost:27017/imgManager" 
mongoose.connect(`mongodb://${dbUrl}`, dbOptions);

edited Mar 10 '19 at 13:13

answered Mar 10 '19 at 12:59

Ele

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2

Surely `dbOptions` should be an object, `{ useNewUrlParser: true}` – Pointy Mar 10 '19 at 13:01

Right syntax for extrapolating a variable with javascript template literals?

3 Answers3