Problem with default parameter and object

Question

I've got a problem with default parameters in Javascript. I have a function like this:

function search(filterOptions = {
    foo: 'bar',
    foo2: 'bar2'
}) {
  ...
}

When I call search() without arguments, filterOptions is set to {foo: 'bar', foo2: 'bar'}, but when I call search({ foo: 'something' }), foo2 is undefined.

I cannot separate filterOptions into several arguments because options are independent.

How can i make foo2 take its default value anyway (and cleanly)?

(I'm on nodejs)

Thank you!

Your parameter is filterOptions and not foo2. Add a validation step like if(!filterOptions.foo2) filterOptions.foo2 = '' would be appropriate — aksappy
– aksappy, Commented Jan 31, 2020 at 16:13

Tyler Roper · Accepted Answer · 2020-01-31 16:17:29Z

1

You could define the defaults within the function and use the spread syntax to combine the two objects, which will override the defaults where applicable.

function search(filterOptions) {
  const defaults = { foo: 'foo', foo2: 'bar' };
  filterOptions = {...defaults,...filterOptions};
  console.log(filterOptions);
}

search({foo: 'something'});

edited Jan 31, 2020 at 16:17

answered Jan 31, 2020 at 16:14

Tyler Roper

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1 Comment

Tyler Roper Over a year ago

@RomainC I've added a link to the relevant portion of the documentation.

Pointy · Accepted Answer · 2020-01-31 16:17:29Z

1

You can provide default values in the parameter list:

    function search({ foo = "bar", foo2 = "bar2"} = {}) {
      console.log("foo is " + foo + ", foo2 is " + foo2);
    }

    console.log(search());
    console.log(search({ foo: "broccoli" }));
    console.log(search({ foo: "my foo", foo2: "my foo2" }));

The = {} at the end is to handle the case when the function is called with no parameters.

answered Jan 31, 2020 at 16:17

Pointy

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Comments

Angshu31 · Accepted Answer · 2020-01-31 17:52:03Z

0

You can define the default variable with an if statement:

function search(arr) {
    if(arr.bar === undefined) {
      arr.bar = "bar1";
    }
    //do whatever
}

The use of === is to make sure that the if does not run if bar is set to "undefined" (a string).

answered Jan 31, 2020 at 17:52

Angshu31

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