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.
Default parameters
Consider the round() function, which rounds an integer:
const result = round(10.25, 0); // 10
We pass two parameters to it: the number to round and the precision of rounding. 0 means that it will round to an integer, and the decimal part will simply be discarded.
In most cases, we need to round exactly to an integer (and not to tenths, for example), so designers of the round() function have made the second parameter optional and set it to a default value of 0. So, you can choose to not specify the second parameter and the result will be the same:
const result = round(10.25); // 10
We can specify precision by passing another parameter:
// rounding to one decimal place
const result = round(10.25, 1); // 10.3
If a JavaScript function accepts optional arguments, they always come after the required ones. Their number varies depending on the function itself, but they always go next to each other and at the end of the list of arguments.
