Consider using arrow functions for callbacks JS-0241
Anti-pattern
Minor
5 months ago
—
a year old
Unexpected function expression
47/* This is an example for calling this function:
48signOut(); */
49export async function signOut() {
50 document.cookie.split(";").forEach(function (c) { 51 document.cookie = c 52 .replace(/^ +/, "") 53 .replace(/=.*/, "=;expires=" + new Date().toUTCString() + ";path=/"); // Sets every cookie as expired to delete them 54 }); 55 await goto("/");
56 location.reload();
57}Unexpected function expression
3/* This is an example for calling this function: getCookie('cookieName'); */
4export function getCookie(cookieName) {
5 const cookie = {};
6 document.cookie.split(";").forEach(function (el) { 7 const [key, value] = el.split("="); 8 cookie[key.trim()] = value; 9 }); 10 return cookie[cookieName];
11}
12
Description
It is recommended to use arrow functions as callbacks.
Arrow functions can be an attractive alternative to function expressions for callbacks or function arguments.
For example, arrow functions are automatically bound to their surrounding scope/context. This provides an alternative to the pre-ES6 standard of explicitly binding function expressions to achieve similar behavior.
Additionally, arrow functions are:
less verbose, and easier to reason about.
bound lexically regardless of where or when they are invoked.
Bad Practice
func(function(a) { return a; }); // ERROR
// prefer: func(a => a)
func(function() { return this.a; }.bind(this)); // ERROR
// prefer: func(() => this.a)
Recommended
// arrow function callback
func(a => a); // OK
// generator as callback
func(function*() { yield; }); // OK
// function expression not used as callback or function argument
var funcVar = function func(a) { return a; }; // OK
// unbound function expression callback
func(function() { return this.a; }); // OK
// recursive named function callback
func(function recursiveFunc(n) { return n && n + recursiveFunc(n - 1); }); // OK