Inputs to functions are known as parameters when a function is declared or defined. Parameters are variables declared in the function signature that can be used inside the function body. When the function is called, these parameters will have the value of whatever is passed in as arguments. It is possible to define a function without parameters.
Functions return values using the
return ends function execution and returns the specified value to the location where it was called. A common mistake is to forget the
return keyword, but without using it in functions, information doesn’t get passed back to us.
Function declarations are used to create named functions. These functions can be called using their declared name. Function declarations are built from: the
function keyword, the function name, a comma-separated list of parameters enclosed by a set of parentheses
(), and a function body enclosed in a set of curly braces
function keyword, or as an arrow function. See the code example for the difference between a named function and an anonymous function.
Function expressions create functions inside an expression instead of as a function declaration. They can be anonymous or assigned to a variable.
Arrow function expressions were introduced in ES6. These expressions are clean and concise. The syntax for an arrow function expression does not require the
function keyword and uses a fat arrow
=> to separate the parameter(s) from the body. There are several variations of arrow functions:
- Arrow functions with a single argument do not require
()around the parameter list .
- Arrow functions with a single expression can use the concise function body which returns the result of the expression without the
- 1When first learning how to calculate the area of a rectangle, there’s a sequence of steps to calculate the correct answer: 1. Measure the width of the rectangle. 2. Measure the height of the rec…
- 3As we saw in previous exercises, a function declaration binds a function to an identifier. However, a function declaration does not ask the code inside the function body to run, it just declares …
- 4So far, the functions we’ve created execute a task without an input. However, some functions can take inputs and use the inputs to perform a task. When declaring a function, we can specify its _par…
- 5One of the features added in ES6 is the ability to use default parameters. Default parameters allow parameters to have a predetermined value in case there is no argument passed into the function …
- 6When a function is called, the computer will run through the function’s code and evaluate the result of calling the function. By default that resulting value is undefined. function rectangleArea(w…
- 7We can also use the return value of a function inside another function. These functions being called within another function are often referred to as helper functions. Since each function is carr…
- 8Another way to define a function is to use a function expression. To define a function inside an expression, we can use the function keyword. In a function expression, the function name is usuall…
- 9ES6 introduced arrow function syntax, a shorter way to write functions by using the special “fat arrow” () => notation. Arrow functions remove the need to type out the keyword function every t…
- 11Give yourself a pat on the back, you just navigated through functions! In this lesson, we covered some important concepts about functions: * A function is a reusable block of code that group…
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