JS-0239 · Consider using `let` or `const` instead of `var`

Consider using let or const instead of var JS-0239

Anti-pattern

Major

2 years ago — 2 years old

Unexpected var, use let or const instead

public/js/resources_js_Pages_Login_jsx.js

15
16
17var Home = function Home() {
18  var foo = "React";19  var bar = "TypeScript";
20  return /*#__PURE__*/react__WEBPACK_IMPORTED_MODULE_0__.createElement("h1", null, "Hello ", foo, " + ", bar);
21};

Unexpected var, use let or const instead

public/js/resources_js_Pages_Login_jsx.js

14/* harmony import */ var react__WEBPACK_IMPORTED_MODULE_0__ = __webpack_require__(/*! react */ "./node_modules/react/index.js");
15
16
17var Home = function Home() {18  var foo = "React";19  var bar = "TypeScript";20  return /*#__PURE__*/react__WEBPACK_IMPORTED_MODULE_0__.createElement("h1", null, "Hello ", foo, " + ", bar);21};22
23/* harmony default export */ const __WEBPACK_DEFAULT_EXPORT__ = (Home);
24

Unexpected var, use let or const instead

public/js/resources_js_Pages_Login_jsx.js

16
17var Home = function Home() {
18  var foo = "React";
19  var bar = "TypeScript";20  return /*#__PURE__*/react__WEBPACK_IMPORTED_MODULE_0__.createElement("h1", null, "Hello ", foo, " + ", bar);
21};
22

Unexpected var, use let or const instead

public/js/resources_js_Pages_Login_jsx.js

11/* harmony export */ __webpack_require__.d(__webpack_exports__, {
12/* harmony export */   "default": () => (__WEBPACK_DEFAULT_EXPORT__)
13/* harmony export */ });
14/* harmony import */ var react__WEBPACK_IMPORTED_MODULE_0__ = __webpack_require__(/*! react */ "./node_modules/react/index.js");15
16
17var Home = function Home() {

Unexpected var, use let or const instead

public/js/resources_js_Pages_Home_jsx.js

16
17var Home = function Home() {
18  var foo = "React";
19  var bar = "TypeScript";20  return /*#__PURE__*/react__WEBPACK_IMPORTED_MODULE_0__.createElement("h1", null, "Hello ", foo, " + ", bar);
21};
22

Description

It is recommended to use let or const over var. This will help prevent re-declaration of variables that are in the global scope when using var.

ES6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as this one:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Block scoped variables shadow outer declarations instead of writing to them.

NOTE: There are certain edge cases where users might want to consider var. Consider this example:

var lib = lib || { run: () => {} }

Here, lib might be a library that is exposed to an HTML file using a <script> tag. The var keyword helps avoid re-writing lib if it has already been declared via an injected script that was executed before this one. Ideally, you should let bundlers worry about cases like this. But if you want to use var anyway, consider using a skipcq comment, or disabling the issue altogether.

Bad Practice

var x = "y";
var CONFIG = {};

kashi326 / inertia-react-laravel-template

Bad Practice

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