A function can accept one or more parameters.
const dosomething = () => {
//do something
}
const dosomethingElse = foo => {
//do something
}
const dosomethingElseAgain = (foo, bar) => {
//do something
}
Starting with ES6/ES2015, functions can have default values for the parameters:
const dosomething = (foo = 1, bar = 'hey') => {
//do something
}
This allows you to call a function without filling all the parameters:
dosomething(3)
dosomething()
ES2018 introduced trailing commas for parameters, a feature that helps reducing bugs due to missing commas when moving around parameters (e.g. moving the last in the middle):
const dosomething = (foo = 1, bar = 'hey') => {
//do something
}
dosomething(2, 'ho!')
You can wrap all your arguments in an array, and use the spread operator when calling the function:
const dosomething = (foo = 1, bar = 'hey') => {
//do something
}
const args = [2, 'ho!']
dosomething(...args)
With many parameters, remembering the order can be difficult. Using objects, destructuring allows to keep the parameter names:
const dosomething = ({ foo = 1, bar = 'hey' }) => {
//do something
console.log(foo) // 2
console.log(bar) // 'ho!'
}
const args = { foo: 2, bar: 'ho!' }
dosomething(args)
Functions now support default parameters:
const foo = function(index = 0, testing = true) { /* ... */ }
foo()
Default parameter values have been introduced in ES2015, and are widely implemented in modern browsers.
This is a doSomething function which accepts param1.
const doSomething = (param1) => {
}
We can add a default value for param1 if the function is invoked without specifying a parameter:
const doSomething = (param1 = 'test') => {
}
This works for more parameters as well, of course:
const doSomething = (param1 = 'test', param2 = 'test2') => {
}
What if you have an unique object with parameters values in it?
Once upon a time, if we had to pass an object of options to a function, in order to have default values of those options if one of them was not defined, you had to add a little bit of code inside the function:
const colorize = (options) => {
if (!options) {
options = {}
}
const color = ('color' in options) ? options.color : 'yellow'
...
}
With object destructuring you can provide default values, which simplifies the code a lot:
const colorize = ({ color = 'yellow' }) => {
...
}
If no object is passed when calling our colorize function, similarly we can assign an empty object by default:
const spin = ({ color = 'yellow' } = {}) => {
...
}