# JavaScript: Function signature

The `Math.pow()`

function, which raises a number to any power, takes two parameters, **a number to raise** and **a power**. If you call `pow()`

without parameters, it returns `NaN`

. The function genuinely tries to perform exponentiation, but with no value passed to it, the interpreter will automatically pass `undefined`

to it. JavaScript forces programmers to be more careful than other languages. In most languages, if you pass fewer parameters to a function than it expects, an error will occur, but this is not the case in JavaScript. `NaN`

will also return when passing any non-numeric values:

```
const result = Math.pow(2, 'boom');
console.log(result); // => NaN
```

Other functions can have different amounts and types of parameters. For example, there may be a function that takes three parameters: a number, a string, and another number.

How do we know how many parameters the `Math.pow()`

function needs and what type the `return`

will be? We took a look at the **signature** of that function. The signature defines the input parameters and their types, as well as the output parameter and its type. You can read about the `Math.pow()`

function in the documentation. In the "Syntax" section, you'll see this:

```
Math.pow(base, exponent)
Parameters
base
The base number.
exponent
The exponent used to raise the base.
```

This is a function signature and a short explanation. The documentation shows you how many arguments the function has and its type, whether the function will return something, and if so, what its return value type will be.

## Instructions

Now it's your turn to find the function signature in the documentation and figure out how to use it.

There is a function in `Math`

called `ceil()`

. Study its documentation.

Write a program using the `Math.ceil()`

function with a constant `number`

, and print the result.

## The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

- Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.

## In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

## My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

## I've read the lessons but nothing is clear 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.

## Definitions

Function signature is a formal description of the parameter and return value types of the function.