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/**
* @fileoverview disallow unncessary concatenation of template strings
* @author Henry Zhu
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
var astUtils = require("../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 === "+";
}
/**
* 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) {
var 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) {
var right = node.right;
while (isConcatenation(right)) {
right = right.left;
}
return right;
}
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
docs: {
description: "disallow unnecessary concatenation of literals or template literals",
category: "Best Practices",
recommended: false
},
schema: []
},
create: function(context) {
return {
BinaryExpression: function(node) {
// check if not concatenation
if (node.operator !== "+") {
return;
}
// account for the `foo + "a" + "b"` case
var left = getLeft(node);
var right = getRight(node);
if (astUtils.isStringLiteral(left) &&
astUtils.isStringLiteral(right) &&
astUtils.isTokenOnSameLine(left, right)
) {
// move warning location to operator
var operatorToken = context.getTokenAfter(left);
while (operatorToken.value !== "+") {
operatorToken = context.getTokenAfter(operatorToken);
}
context.report(
node,
operatorToken.loc.start,
"Unexpected string concatenation of literals.");
}
}
};
}
};
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