/**
* @fileoverview Rule to require braces in arrow function body.
* @author Alberto RodrÃguez
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
const astUtils = require("../ast-utils");
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
docs: {
description: "require braces around arrow function bodies",
category: "ECMAScript 6",
recommended: false,
url: "https://eslint.org/docs/rules/arrow-body-style"
},
schema: {
anyOf: [
{
type: "array",
items: [
{
enum: ["always", "never"]
}
],
minItems: 0,
maxItems: 1
},
{
type: "array",
items: [
{
enum: ["as-needed"]
},
{
type: "object",
properties: {
requireReturnForObjectLiteral: { type: "boolean" }
},
additionalProperties: false
}
],
minItems: 0,
maxItems: 2
}
]
},
fixable: "code"
},
create(context) {
const options = context.options;
const always = options[0] === "always";
const asNeeded = !options[0] || options[0] === "as-needed";
const never = options[0] === "never";
const requireReturnForObjectLiteral = options[1] && options[1].requireReturnForObjectLiteral;
const sourceCode = context.getSourceCode();
/**
* Checks whether the given node has ASI problem or not.
* @param {Token} token The token to check.
* @returns {boolean} `true` if it changes semantics if `;` or `}` followed by the token are removed.
*/
function hasASIProblem(token) {
return token && token.type === "Punctuator" && /^[([/`+-]/.test(token.value);
}
/**
* Gets the closing parenthesis which is the pair of the given opening parenthesis.
* @param {Token} token The opening parenthesis token to get.
* @returns {Token} The found closing parenthesis token.
*/
function findClosingParen(token) {
let node = sourceCode.getNodeByRangeIndex(token.range[1]);
while (!astUtils.isParenthesised(sourceCode, node)) {
node = node.parent;
}
return sourceCode.getTokenAfter(node);
}
/**
* Determines whether a arrow function body needs braces
* @param {ASTNode} node The arrow function node.
* @returns {void}
*/
function validate(node) {
const arrowBody = node.body;
if (arrowBody.type === "BlockStatement") {
const blockBody = arrowBody.body;
if (blockBody.length !== 1 && !never) {
return;
}
if (asNeeded && requireReturnForObjectLiteral && blockBody[0].type === "ReturnStatement" &&
blockBody[0].argument && blockBody[0].argument.type === "ObjectExpression") {
return;
}
if (never || asNeeded && blockBody[0].type === "ReturnStatement") {
let message;
if (blockBody.length === 0) {
message = "Unexpected block statement surrounding arrow body; put a value of `undefined` immediately after the `=>`.";
} else if (blockBody.length > 1) {
message = "Unexpected block statement surrounding arrow body.";
} else if (astUtils.isOpeningBraceToken(sourceCode.getFirstToken(blockBody[0], { skip: 1 }))) {
message = "Unexpected block statement surrounding arrow body; parenthesize the returned value and move it immediately after the `=>`.";
} else {
message = "Unexpected block statement surrounding arrow body; move the returned value immediately after the `=>`.";
}
context.report({
node,
loc: arrowBody.loc.start,
message,
fix(fixer) {
const fixes = [];
if (blockBody.length !== 1 ||
blockBody[0].type !== "ReturnStatement" ||
!blockBody[0].argument ||
hasASIProblem(sourceCode.getTokenAfter(arrowBody))
) {
return fixes;
}
const openingBrace = sourceCode.getFirstToken(arrowBody);
const closingBrace = sourceCode.getLastToken(arrowBody);
const firstValueToken = sourceCode.getFirstToken(blockBody[0], 1);
const lastValueToken = sourceCode.getLastToken(blockBody[0]);
const commentsExist =
sourceCode.commentsExistBetween(openingBrace, firstValueToken) ||
sourceCode.commentsExistBetween(lastValueToken, closingBrace);
/*
* Remove tokens around the return value.
* If comments don't exist, remove extra spaces as well.
*/
if (commentsExist) {
fixes.push(
fixer.remove(openingBrace),
fixer.remove(closingBrace),
fixer.remove(sourceCode.getTokenAfter(openingBrace)) // return keyword
);
} else {
fixes.push(
fixer.removeRange([openingBrace.range[0], firstValueToken.range[0]]),
fixer.removeRange([lastValueToken.range[1], closingBrace.range[1]])
);
}
/*
* If the first token of the reutrn value is `{`,
* enclose the return value by parentheses to avoid syntax error.
*/
if (astUtils.isOpeningBraceToken(firstValueToken)) {
fixes.push(
fixer.insertTextBefore(firstValueToken, "("),
fixer.insertTextAfter(lastValueToken, ")")
);
}
/*
* If the last token of the return statement is semicolon, remove it.
* Non-block arrow body is an expression, not a statement.
*/
if (astUtils.isSemicolonToken(lastValueToken)) {
fixes.push(fixer.remove(lastValueToken));
}
return fixes;
}
});
}
} else {
if (always || (asNeeded && requireReturnForObjectLiteral && arrowBody.type === "ObjectExpression")) {
context.report({
node,
loc: arrowBody.loc.start,
message: "Expected block statement surrounding arrow body.",
fix(fixer) {
const fixes = [];
const arrowToken = sourceCode.getTokenBefore(arrowBody, astUtils.isArrowToken);
const firstBodyToken = sourceCode.getTokenAfter(arrowToken);
const lastBodyToken = sourceCode.getLastToken(node);
const isParenthesisedObjectLiteral =
astUtils.isOpeningParenToken(firstBodyToken) &&
astUtils.isOpeningBraceToken(sourceCode.getTokenAfter(firstBodyToken));
// Wrap the value by a block and a return statement.
fixes.push(
fixer.insertTextBefore(firstBodyToken, "{return "),
fixer.insertTextAfter(lastBodyToken, "}")
);
// If the value is object literal, remove parentheses which were forced by syntax.
if (isParenthesisedObjectLiteral) {
fixes.push(
fixer.remove(firstBodyToken),
fixer.remove(findClosingParen(firstBodyToken))
);
}
return fixes;
}
});
}
}
}
return {
"ArrowFunctionExpression:exit": validate
};
}
};