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150

Javascript : optional parameters in function

rated 0 times [ 153] [ 3] / answers: 1 / hits: 27281 / 8 Years ago, thu, august 25, 2016, 12:00:00

Let's say I have this :

function concatenate(a, b, c) {

    // Concatenate a, b, and c

}

How do I handle those calls ?

x = concatenate(a)



x = concatenate(a, b)



x = concatenate(a, c)

How can I make my function aware of the parameter I gave to it ?

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rafael

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3 Years ago

answered 8 Years ago tylerdamiena · Accepted Answer

Any unfilled argument will be undefined.

concatenate(a, c) is equivalent to concatenate(a, b). You cannot pass the third parameter without passing the second; but you can pass undefined (or null, I suppose) explicitly: concatenate(a, undefined, c).

In the function, you can check for undefined and replace with a default value.

Alternately, you can use an object argument to imitate keyword arguments: concatenate({a: a, c: c}).