| /** |
| * @fileoverview disallow unncessary concatenation of template strings |
| * @author Henry Zhu |
| */ |
| "use strict"; |
| |
| //------------------------------------------------------------------------------ |
| // Requirements |
| //------------------------------------------------------------------------------ |
| |
| const astUtils = require("./utils/ast-utils"); |
| |
| //------------------------------------------------------------------------------ |
| // Helpers |
| //------------------------------------------------------------------------------ |
| |
| /** |
| * Checks whether or not a given node is a concatenation. |
| * @param {ASTNode} node - A node to check. |
| * @returns {boolean} `true` if the node is a concatenation. |
| */ |
| function isConcatenation(node) { |
| return node.type === "BinaryExpression" && node.operator === "+"; |
| } |
| |
| /** |
| * Checks if the given token is a `+` token or not. |
| * @param {Token} token - The token to check. |
| * @returns {boolean} `true` if the token is a `+` token. |
| */ |
| function isConcatOperatorToken(token) { |
| return token.value === "+" && token.type === "Punctuator"; |
| } |
| |
| /** |
| * Get's the right most node on the left side of a BinaryExpression with + operator. |
| * @param {ASTNode} node - A BinaryExpression node to check. |
| * @returns {ASTNode} node |
| */ |
| function getLeft(node) { |
| let left = node.left; |
| |
| while (isConcatenation(left)) { |
| left = left.right; |
| } |
| return left; |
| } |
| |
| /** |
| * Get's the left most node on the right side of a BinaryExpression with + operator. |
| * @param {ASTNode} node - A BinaryExpression node to check. |
| * @returns {ASTNode} node |
| */ |
| function getRight(node) { |
| let right = node.right; |
| |
| while (isConcatenation(right)) { |
| right = right.left; |
| } |
| return right; |
| } |
| |
| //------------------------------------------------------------------------------ |
| // Rule Definition |
| //------------------------------------------------------------------------------ |
| |
| module.exports = { |
| meta: { |
| type: "suggestion", |
| |
| docs: { |
| description: "disallow unnecessary concatenation of literals or template literals", |
| category: "Best Practices", |
| recommended: false, |
| url: "https://eslint.org/docs/rules/no-useless-concat" |
| }, |
| |
| schema: [] |
| }, |
| |
| create(context) { |
| const sourceCode = context.getSourceCode(); |
| |
| return { |
| BinaryExpression(node) { |
| |
| // check if not concatenation |
| if (node.operator !== "+") { |
| return; |
| } |
| |
| // account for the `foo + "a" + "b"` case |
| const left = getLeft(node); |
| const right = getRight(node); |
| |
| if (astUtils.isStringLiteral(left) && |
| astUtils.isStringLiteral(right) && |
| astUtils.isTokenOnSameLine(left, right) |
| ) { |
| const operatorToken = sourceCode.getFirstTokenBetween(left, right, isConcatOperatorToken); |
| |
| context.report({ |
| node, |
| loc: operatorToken.loc.start, |
| message: "Unexpected string concatenation of literals." |
| }); |
| } |
| } |
| }; |
| } |
| }; |