How to override default parameter in JavaScript

Question

I've found lots of creative ways to set default parameters in ES5 & ES6 but I have yet to see a simple example of how to override default parameters in JavaScript. Take this example:

new Connection(host, port = 25575, password, timeout = 5000)

The default timeout is fine but the port number is not. When calling this function, JavaScript always treats the second parameter as the password parameter:

myConnection = connFactory.getConnection(process.env.IP,
                                         process.env.PORT,
                                         process.env.PASSWORD)

This code results in an authentication error because the second parameter is assumed to be password. How can I override the default parameter for port without modifying the original function definition?

new Connection(host, port = 25575, password, timeout = 5000) what kind of syntax is this? Can you show us a more complete example of your code? We have no idea what getConnection looks like, so how can we help you with it? — JLRishe
– JLRishe, Commented Dec 20, 2017 at 14:34
Wrap the function in your own function, which allows you to change the order of parameters. — user5734311
– user5734311, Commented Dec 20, 2017 at 14:34
This should not be that case. In this fiddle, the default parameter are corretly use and the second parameter is used as port. So I would guess the problem is somewhere else. Please create a minimal example that allows to reproduce the problem. — t.niese
– t.niese, Commented Dec 20, 2017 at 14:34
how does getConnection look like? It sounds like there is something wrong into getConnection rather than default values — Facundo La Rocca
– Facundo La Rocca, Commented Dec 20, 2017 at 14:36
I believe the question is about parameter's ordering rather than overriding default parameter value — The Reason
– The Reason, Commented Dec 20, 2017 at 14:36

The Reason · Accepted Answer · 2017-12-20 14:34:59Z

5

You may use a config object as a parameter for your function. For example:

function foo({a='SO', b}) {
  console.log(a, b)
}

foo({b: 'Yeap', a: 'baz'}) // baz Yeap
foo({b: 'foo'}) // SO foo

It will guarantee your ordering.

answered Dec 20, 2017 at 14:34

The Reason

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Comments

elzoy · Accepted Answer · 2017-12-20 15:23:16Z

0

Assuming that 'getConnection' isn't your function but comes from some unreachable for you place, here is one of a few solutions that will guarantee to be working. It is a function which task is to prepare all parameters.

function getConnectionRunner(host, password, optional = {port: 25575, timeout: 5000}) {
  const port = optional.port || 25575;
  const timeout = optional.timeout || 5000;

  connFactory.getConnection(host, port, password, timeout);
}

edited Dec 20, 2017 at 15:23

answered Dec 20, 2017 at 15:07

elzoy

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