docs: replace var with let or const in rules docs (#19396)

* docs: replace var with let or const in rules docs

* docs: update global variable

docs/src/rules/no-new.md

@@ -7,7 +7,7 @@ rule_type: suggestion
 The goal of using `new` with a constructor is typically to create an object of a particular type and store that object in a variable, such as:
 
 ```js
-var person = new Person();
+const person = new Person();
 ```
 
 It's less common to use `new` and not store the result, such as:
@@ -41,7 +41,7 @@ Examples of **correct** code for this rule:
 ```js
 /*eslint no-new: "error"*/
 
-var thing = new Thing();
+const thing = new Thing();
 
 Foo();
 ```

docs/src/rules/no-unused-expressions.md

@@ -15,11 +15,11 @@ This rule aims to eliminate unused expressions which have no effect on the state
 This rule does not apply to function calls or constructor calls with the `new` operator, because they could have *side effects* on the state of the program.
 
 ```js
-var i = 0;
+let i = 0;
 function increment() { i += 1; }
 increment(); // return value is unused, but i changed as a side effect
 
-var nThings = 0;
+let nThings = 0;
 function Thing() { nThings += 1; }
 new Thing(); // constructed object is unused, but nThings changed as a side effect
 ```
@@ -270,9 +270,9 @@ Examples of **correct** code for the `{ "enforceForJSX": true }` option:
 ```jsx
 /*eslint no-unused-expressions: ["error", { "enforceForJSX": true }]*/
 
-var myComponentPartial = <MyComponent />;
+const myComponentPartial = <MyComponent />;
 
-var myFragment = <></>;
+const myFragment = <></>;
 ```
 
 :::

docs/src/rules/no-unused-vars.md

@@ -16,11 +16,11 @@ This rule is aimed at eliminating unused variables, functions, and function para
 A variable `foo` is considered to be used if any of the following are true:
 
 * It is called (`foo()`) or constructed (`new foo()`)
-* It is read (`var bar = foo`)
+* It is read (`let bar = foo`)
 * It is passed into a function as an argument (`doSomething(foo)`)
 * It is read inside of a function that is passed to another function (`doSomething(function() { foo(); })`)
 
-A variable is *not* considered to be used if it is only ever declared (`var foo = 5`) or assigned to (`foo = 7`).
+A variable is *not* considered to be used if it is only ever declared (`let foo = 5`) or assigned to (`foo = 7`).
 
 Examples of **incorrect** code for this rule:
 
@@ -33,14 +33,14 @@ Examples of **incorrect** code for this rule:
 // It checks variables you have defined as global
 some_unused_var = 42;
 
-var x;
+let x;
 
 // Write-only variables are not considered as used.
-var y = 10;
+let y = 10;
 y = 5;
 
 // A read for a modification of itself is not considered as used.
-var z = 0;
+let z = 0;
 z = z + 1;
 
 // By default, unused arguments cause warnings.
@@ -70,7 +70,7 @@ Examples of **correct** code for this rule:
 ```js
 /*eslint no-unused-vars: "error"*/
 
-var x = 10;
+const x = 10;
 alert(x);
 
 // foo is considered used here
@@ -180,8 +180,8 @@ Examples of **correct** code for the `{ "varsIgnorePattern": "[iI]gnored" }` opt
 ```js
 /*eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]*/
 
-var firstVarIgnored = 1;
-var secondVar = 2;
+const firstVarIgnored = 1;
+const secondVar = 2;
 console.log(secondVar);
 ```
 
@@ -404,12 +404,12 @@ Examples of **correct** code for the `{ "ignoreRestSiblings": true }` option:
 /*eslint no-unused-vars: ["error", { "ignoreRestSiblings": true }]*/
 
 // 'foo' and 'bar' were ignored because they have a rest property sibling.
-var { foo, ...rest } = data;
+const { foo, ...rest } = data;
 console.log(rest);
 
 // OR
 
-var bar;
+let bar;
 ({ bar, ...rest } = data);
 ```
 
@@ -474,8 +474,8 @@ Examples of **incorrect** code for the `{ "reportUsedIgnorePattern": true }` opt
 ```js
 /*eslint no-unused-vars: ["error", { "reportUsedIgnorePattern": true, "varsIgnorePattern": "[iI]gnored" }]*/
 
-var firstVarIgnored = 1;
-var secondVar = 2;
+const firstVarIgnored = 1;
+const secondVar = 2;
 console.log(firstVarIgnored, secondVar);
 ```
 
@@ -488,8 +488,8 @@ Examples of **correct** code for the `{ "reportUsedIgnorePattern": true }` optio
 ```js
 /*eslint no-unused-vars: ["error", { "reportUsedIgnorePattern": true, "varsIgnorePattern": "[iI]gnored" }]*/
 
-var firstVar = 1;
-var secondVar = 2;
+const firstVar = 1;
+const secondVar = 2;
 console.log(firstVar, secondVar);
 ```
 

docs/src/rules/no-void.md

@@ -43,7 +43,7 @@ foo = undefined;
 When used with IIFE (immediately-invoked function expression), `void` can be used to force the function keyword to be treated as an expression instead of a declaration:
 
 ```js
-var foo = 1;
+let foo = 1;
 void function(){ foo = 1; }() // will assign foo a value of 1
 +function(){ foo = 1; }() // same as above
 ```
@@ -68,7 +68,7 @@ Examples of **incorrect** code for this rule:
 void foo
 void someFunction();
 
-var foo = void bar();
+const foo = void bar();
 function baz() {
     return void 0;
 }
@@ -93,7 +93,7 @@ Examples of **incorrect** code for `{ "allowAsStatement": true }`:
 ```js
 /*eslint no-void: ["error", { "allowAsStatement": true }]*/
 
-var foo = void bar();
+const foo = void bar();
 function baz() {
     return void 0;
 }

docs/src/rules/prefer-arrow-callback.md

@@ -53,7 +53,7 @@ foo(a => a); // OK
 foo(function*() { yield; }); // OK
 
 // function expression not used as callback or function argument
-var foo = function foo(a) { return a; }; // OK
+const foo = function foo(a) { return a; }; // OK
 
 // unbound function expression callback
 foo(function() { return this.a; }); // OK