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Add prefer-bigint-literals rule (#2722)
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‎docs/rules/prefer-bigint-literals.md‎

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# Prefer `BigInt` literals over the constructor
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💼 This rule is enabled in the ✅ `recommended` [config](https://github.com/sindresorhus/eslint-plugin-unicorn#recommended-config).
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🔧💡 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix) and manually fixable by [editor suggestions](https://eslint.org/docs/latest/use/core-concepts#rule-suggestions).
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<!-- end auto-generated rule header -->
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<!-- Do not manually modify this header. Run: `npm run fix:eslint-docs` -->
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Use `1n` instead of `BigInt(1)`.
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## Examples
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```js
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// ❌
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const bigint = BigInt(1);
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// ✅
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const bigint = 1n;
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```
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```js
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// ❌
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const bigint = BigInt('1');
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// ✅
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const bigint = 1n;
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```

‎readme.md‎

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| [prefer-array-index-of](docs/rules/prefer-array-index-of.md) | Prefer `Array#{indexOf,lastIndexOf}()` over `Array#{findIndex,findLastIndex}()` when looking for the index of an item. | ✅ | 🔧 | 💡 |
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| [prefer-array-some](docs/rules/prefer-array-some.md) | Prefer `.some(…)` over `.filter(…).length` check and `.{find,findLast,findIndex,findLastIndex}(…)`. | ✅ | 🔧 | 💡 |
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| [prefer-at](docs/rules/prefer-at.md) | Prefer `.at()` method for index access and `String#charAt()`. | ✅ | 🔧 | 💡 |
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| [prefer-bigint-literals](docs/rules/prefer-bigint-literals.md) | Prefer `BigInt` literals over the constructor. | ✅ | 🔧 | 💡 |
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| [prefer-blob-reading-methods](docs/rules/prefer-blob-reading-methods.md) | Prefer `Blob#arrayBuffer()` over `FileReader#readAsArrayBuffer(…)` and `Blob#text()` over `FileReader#readAsText(…)`. | ✅ | | |
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| [prefer-class-fields](docs/rules/prefer-class-fields.md) | Prefer class field declarations over `this` assignments in constructors. | ✅ | 🔧 | 💡 |
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| [prefer-code-point](docs/rules/prefer-code-point.md) | Prefer `String#codePointAt(…)` over `String#charCodeAt(…)` and `String.fromCodePoint(…)` over `String.fromCharCode(…)`. | ✅ | | 💡 |

‎rules/index.js‎

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export {default as 'prefer-array-index-of'} from './prefer-array-index-of.js';
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export {default as 'prefer-array-some'} from './prefer-array-some.js';
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export {default as 'prefer-at'} from './prefer-at.js';
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export {default as 'prefer-bigint-literals'} from './prefer-bigint-literals.js';
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export {default as 'prefer-blob-reading-methods'} from './prefer-blob-reading-methods.js';
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export {default as 'prefer-class-fields'} from './prefer-class-fields.js';
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export {default as 'prefer-code-point'} from './prefer-code-point.js';

‎rules/prefer-bigint-literals.js‎

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import {
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isCallExpression,
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isStringLiteral,
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} from './ast/index.js';
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const MESSAGE_ID_ERROR = 'prefer-bigint-literals/error';
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const MESSAGE_ID_SUGGESTION = 'prefer-bigint-literals/suggestion';
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const messages = {
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[MESSAGE_ID_ERROR]: 'Prefer using bigint literal over `BigInt(…)`.',
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[MESSAGE_ID_SUGGESTION]: 'Replace with {{replacement}}.',
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};
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const canUseNumericLiteralRaw = numericLiteral => {
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const raw = numericLiteral.raw.replaceAll('_', '').toLowerCase();
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if (raw.includes('.')) {
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return false;
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}
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const {value} = numericLiteral;
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for (const {prefix, base} of [
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{prefix: '0b', base: 2},
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{prefix: '0o', base: 8},
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{prefix: '0x', base: 16},
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]) {
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if (raw.startsWith(prefix)) {
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return raw.slice(2) === value.toString(base);
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}
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}
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if (raw.includes('e')) {
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return false;
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}
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return raw === String(value);
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};
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function getReplacement(valueNode) {
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if (isStringLiteral(valueNode)) {
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const raw = valueNode.raw.slice(1, -1);
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try {
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BigInt(raw);
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} catch {
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return;
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}
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return {shouldUseSuggestion: false, text: `${raw.trimEnd()}n`};
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}
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const {value, raw} = valueNode;
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if (!Number.isInteger(value)) {
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return;
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}
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let bigint;
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try {
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bigint = BigInt(value);
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} catch {
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return;
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}
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const shouldUseSuggestion = !canUseNumericLiteralRaw(valueNode);
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const text = shouldUseSuggestion ? `${bigint}n` : `${raw}n`;
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return {shouldUseSuggestion, text};
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}
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/** @param {import('eslint').Rule.RuleContext} context */
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const create = context => ({
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CallExpression(callExpression) {
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if (!isCallExpression(callExpression, {
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name: 'BigInt',
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argumentsLength: 1,
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optional: false,
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})) {
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return;
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}
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const [valueNode] = callExpression.arguments;
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const replacement = getReplacement(valueNode);
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if (!replacement) {
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return;
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}
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const problem = {
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node: callExpression,
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messageId: MESSAGE_ID_ERROR,
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};
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const {shouldUseSuggestion, text} = replacement;
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/** @param {import('eslint').Rule.RuleFixer} fixer */
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const fix = fixer => fixer.replaceText(callExpression, text);
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if (shouldUseSuggestion || context.sourceCode.getCommentsInside(callExpression).length > 0) {
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problem.suggest = [
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{
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messageId: MESSAGE_ID_SUGGESTION,
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data: {
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replacement: text.length < 20 ? `\`${text}\`` : 'a bigint literal',
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},
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fix,
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},
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];
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} else {
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problem.fix = fix;
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}
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return problem;
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},
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});
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/** @type {import('eslint').Rule.RuleModule} */
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const config = {
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create,
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meta: {
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type: 'suggestion',
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docs: {
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description: 'Prefer `BigInt` literals over the constructor.',
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recommended: true,
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},
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fixable: 'code',
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hasSuggestions: true,
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messages,
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},
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};
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export default config;

‎test/prefer-bigint-literals.js‎

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import {getTester} from './utils/test.js';
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const {test} = getTester(import.meta);
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test.snapshot({
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valid: [
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'1n',
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'BigInt()',
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'BigInt(1, 1)',
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'BigInt(...[1])',
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'BigInt(true)',
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'BigInt(null)',
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'new BigInt(1)',
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'Not_BigInt(1)',
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'BigInt("1.0")',
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'BigInt("1.1")',
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'BigInt("1e3")',
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'BigInt(`1`)',
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'BigInt("1" + "2")',
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'BigInt?.(1)',
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'BigInt(1.1)',
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'typeof BigInt',
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'BigInt(1n)',
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'BigInt("not-number")',
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'BigInt("1_2")',
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'BigInt("1\\\n2")',
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'BigInt("1\\\n2")',
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String.raw`BigInt("\u{31}")`,
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],
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invalid: [
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'BigInt("0")',
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'BigInt(" 0 ")',
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'BigInt("9007199254740993")',
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'BigInt("0B11")',
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'BigInt("0O777")',
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'BigInt("0XFe")',
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`BigInt("${'9'.repeat(100)}")`,
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'BigInt(0)',
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'BigInt(0B11_11)',
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'BigInt(0O777_777)',
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'BigInt(0XFe_fE)',
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// Legacy octal literals
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...[
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'BigInt(0777)',
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'BigInt(0888)',
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].map(code => ({code, languageOptions: {sourceType: 'script'}})),
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// Not fixable
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'BigInt(9007199254740993)',
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'BigInt(0x20000000000001)',
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'BigInt(9_007_199_254_740_993)',
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'BigInt(0x20_00_00_00_00_00_01)',
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'BigInt(1.0)',
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'BigInt(1e2)',
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'BigInt(/* comment */1)',
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`BigInt(${'9'.repeat(100)})`,
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],
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});

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