Add prefer-ternary rule

docs/rules/prefer-ternary.md

@@ -0,0 +1,122 @@
+# Prefer ternary expressions over simple `if-else` statements
+
+This rule enforces the use of ternary expressions over  'simple' `if-else` statements, where 'simple' means the consequent and alternate are each one line and have the same basic type and form.
+
+Using an `if-else` statement typically results in more lines of code than a single-line ternary expression, which leads to an unnecessarily larger codebase that is more difficult to maintain.
+
+Additionally, using an `if-else` statement can result in defining variables using `let` or `var` solely to be reassigned within the blocks. This leads to variables being unnecessarily mutable and prevents `prefer-const` from flagging the variable.
+
+This rule is fixable.
+
+## Fail
+
+```js
+function unicorn() {
+	if (test) {
+		return a;
+	} else {
+		return b;
+	}
+}
+```
+
+```js
+function* unicorn() {
+	if (test) {
+		yield a;
+	} else {
+		yield b;
+	}
+}
+```
+
+```js
+async function unicorn() {
+	if (test) {
+		await a();
+	} else {
+		await b();
+	}
+}
+```
+
+```js
+if (test) {
+	throw new Error('foo');
+} else {
+	throw new Error('bar');
+}
+```
+
+```js
+let foo;
+if (test) {
+	foo = 1;
+} else {
+	foo = 2;
+}
+```
+
+## Pass
+
+```js
+function unicorn() {
+	return test ? a : b;
+}
+```
+
+```js
+function* unicorn() {
+	yield (test ? a : b);
+}
+```
+
+```js
+async function unicorn() {
+	await (test ? a() : b());
+}
+```
+
+```js
+const error = test ? new Error('foo') : new Error('bar');
+throw error;
+```
+
+```js
+let foo;
+foo = test ? 1 : 2;
+```
+
+```js
+// Multiple expressions
+let foo;
+let bar;
+if (test) {
+	foo = 1;
+	bar = 2;
+} else{
+	foo = 2;
+}
+```
+
+```js
+// Different expressions
+function unicorn() {
+	if (test) {
+		return a;
+	} else {
+		throw new Error('error');
+	}
+}
+```
+
+```js
+// Assign to different variable
+let foo;
+let bar;
+if (test) {
+	foo = 1;
+} else{
+	baz = 2;
+}
+```

index.js

@@ -70,6 +70,7 @@ module.exports = {
 				'unicorn/prefer-spread': 'error',
 				'unicorn/prefer-starts-ends-with': 'error',
 				'unicorn/prefer-string-slice': 'error',
+				'unicorn/prefer-ternary': 'error',
 				'unicorn/prefer-text-content': 'error',
 				'unicorn/prefer-trim-start-end': 'error',
 				'unicorn/prefer-type-error': 'error',

package.json

@@ -93,6 +93,9 @@
 		"extends": [
 			"plugin:eslint-plugin/all"
 		],
+		"ignores": [
+			"test/integration/{fixtures,unicorn}/**"
+		],
 		"overrides": [
 			{
 				"files": "rules/utils/*.js",

readme.md

@@ -84,6 +84,7 @@ Configure it in `package.json`.
 			"unicorn/prefer-spread": "error",
 			"unicorn/prefer-starts-ends-with": "error",
 			"unicorn/prefer-string-slice": "error",
+			"unicorn/prefer-ternary": "off",
 			"unicorn/prefer-text-content": "error",
 			"unicorn/prefer-trim-start-end": "error",
 			"unicorn/prefer-type-error": "error",
@@ -147,6 +148,7 @@ Configure it in `package.json`.
 - [prefer-spread](docs/rules/prefer-spread.md) - Prefer the spread operator over `Array.from()`. *(fixable)*
 - [prefer-starts-ends-with](docs/rules/prefer-starts-ends-with.md) - Prefer `String#startsWith()` & `String#endsWith()` over more complex alternatives. *(partly fixable)*
 - [prefer-string-slice](docs/rules/prefer-string-slice.md) - Prefer `String#slice()` over `String#substr()` and `String#substring()`. *(partly fixable)*
+- [prefer-ternary](docs/rules/prefer-ternary.md) - Prefer ternary expressions over simple `if-else` statements. *(fixable)*
 - [prefer-text-content](docs/rules/prefer-text-content.md) - Prefer `.textContent` over `.innerText`. *(fixable)*
 - [prefer-trim-start-end](docs/rules/prefer-trim-start-end.md) - Prefer `String#trimStart()` / `String#trimEnd()` over `String#trimLeft()` / `String#trimRight()`. *(fixable)*
 - [prefer-type-error](docs/rules/prefer-type-error.md) - Enforce throwing `TypeError` in type checking conditions. *(fixable)*

rules/no-for-loop.js

@@ -384,11 +384,9 @@ const create = context => {
 					}
 
 					if (elementNode) {
-						if (removeDeclaration) {
-							yield fixer.removeRange(getRemovalRange(elementNode, sourceCode));
-						} else {
-							yield fixer.replaceText(elementNode.init, element);
-						}
+						yield removeDeclaration ?
+							fixer.removeRange(getRemovalRange(elementNode, sourceCode)) :
+							fixer.replaceText(elementNode.init, element);
 					}
 				};
 			}