Prefer var declarations be placed at the top of their scope JS-0102
Anti-pattern
Minor
2 years ago
—
2 years old
All 'var' declarations must be at the top of the function scope
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() {All 'var' declarations must be at the top of the function scope
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);
24All 'var' declarations must be at the top of the function scope
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);
24All 'var' declarations must be at the top of the function scope
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() {All 'var' declarations must be at the top of the function scope
15/* harmony import */ var react__WEBPACK_IMPORTED_MODULE_0___default = /*#__PURE__*/__webpack_require__.n(react__WEBPACK_IMPORTED_MODULE_0__);
16
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18var Home = function Home() {19 var foo = "React";20 var bar = "TypeScript";21 return /*#__PURE__*/react__WEBPACK_IMPORTED_MODULE_0___default().createElement("h1", null, "Hello ", foo, " + ", bar);22};23
24/* harmony default export */ const __WEBPACK_DEFAULT_EXPORT__ = (Home);
25
Description
Declare variables at the top of their scope as it improves code readability, performance and also helps in code navigation.
The vars-on-top rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program. By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter. This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Bad Practice
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
Recommended
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}