CODEWITHSUNDEEP
javascript
knomdlo
knomdlo

Reputation: 408

What is "[," function arguments list in javascript API's

When going through docs or API's of JS libraries, I notice a "[," in params list.

Eg: vega.key(fields[, flat])

Does it mean optional arguments. How to interpret these.

Upvotes: 1

Views: 49

Answers (2)

axiac
axiac

Reputation: 72226

It is a (widely-used) notation in documentation (and only in documentation; it is not valid syntax).

The part [, flat] means the second argument is named flat and it is optional.

The function can be called with two arguments (vega.key(fields, flat)) or with only one argument (vega.key(fields)). In this case, the comma must also be stripped (i.e. calling it as vega.key(fields,) is invalid syntax.

You will also encounter this notation: vega.key(fields[, flat, ...]) or vega.keys(fields[, ...]) that means the function can be invoked with one or more arguments; fields is required in the above notation, the others are optional.

Upvotes: 1

An0num0us
An0num0us

Reputation: 961

It means optional argument. You will often see

someFunc(arg1[, arg2[, arg3]])

which means arg2 and arg3 are optional. When arg2 is passed to the function, arg3 need not be, because it's optional, but arg2 is necessary when arg3 is passed.

Upvotes: 2

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