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| /** | |
| * @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." | |
| }); | |
| } | |
| } | |
| }; | |
| } | |
| }; |