'ageCalculator' was used before it was defined
77 }
78
79 if (name === "dob") {
80 let calculateAge = ageCalculator(e.target.value); 81 calculateAge === null ? (calculateAge = "") : null;
82 setUserInfo((prev) => {
83 return { ...prev, age: calculateAge };'isValidUrl' was used before it was defined
45 };
46
47 const handleAddProfile = () => {
48 if (!newProfile.name || !isValidUrl(newProfile.url)) { 49 alert("Please enter a valid profile name and URL starting with http");
50 return;
51 }
Description
It is recommended to use a variable only after it is defined as it might produce errors at runtime.
In JavaScript, prior to ES6, variable and function declarations are hoisted to the top of a scope, so it's possible to use identifiers before their formal declarations in code. This can be confusing and some believe it is best to always declare variables and functions before using them.
In ES6, block-level bindings (let and const) introduce a "temporal dead zone" where a ReferenceError will be thrown with any attempt to access the variable before its declaration.
Bad Practice
alert(a);
var a = 10;
f();
function f() {}
function g() {
return b;
}
var b = 1;
{
alert(c);
let c = 1;
}
Recommended
var a;
a = 10;
alert(a);
function f() {}
f(1);
var b = 1;
function g() {
return b;
}
{
let c;
c++;
}