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# Function.prototype.length

The **`length`** data property of a `Function` instance indicates the number of parameters expected by the function.

## Value

A number.

## Description

A `Function` object's `length` property indicates how many arguments the function expects, i.e. the number of formal parameters. 

The `Function` constructor is itself a `Function` object. Its `length` data property has a value of `1`.

Due to historical reasons, `Function.prototype` is a callable itself. The `length` property of `Function.prototype` has a value of `0`.
