Variable used before definition JS-0129
Bug risk
Major
15 days ago
—
3 years old
'scope_Self' was used before it was defined
1775 // Left offset of the handle, in relation to the slider
1776 scope_Locations.slice(),
1777 // add the slider public API to an accessible parameter when this is unavailable
1778 scope_Self);1779 });
1780 }
1781 });'scope_Self' was used before it was defined
1763 scope_Events[targetEvent].forEach(function (callback) {
1764 callback.call(
1765 // Use the slider public API as the scope ('this')
1766 scope_Self, 1767 // Return values as array, so arg_1[arg_2] is always valid.
1768 scope_Values.map(options.format.to),
1769 // Handle index, 0 or 1'scope_Self' was used before it was defined
1594 Object.keys(scope_Events).forEach(function (targetEvent) {
1595 if ("hover" === targetEvent.split(".")[0]) {
1596 scope_Events[targetEvent].forEach(function (callback) {
1597 callback.call(scope_Self, value);1598 });
1599 }
1600 });'i' was used before it was defined
4 if (!t[o]) {
5 const a = typeof require === "function" && require;
6 if (!u && a) return a(o, !0);
7 if (i) return i(o, !0); 8 const f = new Error("Cannot find module '" + o + "'");
9 throw ((f.code = "MODULE_NOT_FOUND"), f);
10 }'i' was used before it was defined
4 if (!t[o]) {
5 const a = typeof require === "function" && require;
6 if (!u && a) return a(o, !0);
7 if (i) return i(o, !0); 8 const f = new Error("Cannot find module '" + o + "'");
9 throw ((f.code = "MODULE_NOT_FOUND"), f);
10 }
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++;
}