145 lines
5.0 KiB
JavaScript
145 lines
5.0 KiB
JavaScript
/**
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* @fileoverview Rule to enforce var declarations are only at the top of a function.
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* @author Danny Fritz
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* @author Gyandeep Singh
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*/
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"use strict";
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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module.exports = {
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meta: {
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type: "suggestion",
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docs: {
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description: "require `var` declarations be placed at the top of their containing scope",
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category: "Best Practices",
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recommended: false,
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url: "https://eslint.org/docs/rules/vars-on-top"
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},
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schema: [],
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messages: {
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top: "All 'var' declarations must be at the top of the function scope."
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}
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},
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create(context) {
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//--------------------------------------------------------------------------
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// Helpers
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//--------------------------------------------------------------------------
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// eslint-disable-next-line jsdoc/require-description
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/**
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* @param {ASTNode} node any node
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* @returns {boolean} whether the given node structurally represents a directive
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*/
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function looksLikeDirective(node) {
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return node.type === "ExpressionStatement" &&
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node.expression.type === "Literal" && typeof node.expression.value === "string";
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}
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/**
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* Check to see if its a ES6 import declaration
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* @param {ASTNode} node any node
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* @returns {boolean} whether the given node represents a import declaration
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*/
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function looksLikeImport(node) {
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return node.type === "ImportDeclaration" || node.type === "ImportSpecifier" ||
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node.type === "ImportDefaultSpecifier" || node.type === "ImportNamespaceSpecifier";
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}
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/**
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* Checks whether a given node is a variable declaration or not.
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* @param {ASTNode} node any node
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* @returns {boolean} `true` if the node is a variable declaration.
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*/
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function isVariableDeclaration(node) {
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return (
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node.type === "VariableDeclaration" ||
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(
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node.type === "ExportNamedDeclaration" &&
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node.declaration &&
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node.declaration.type === "VariableDeclaration"
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)
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);
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}
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/**
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* Checks whether this variable is on top of the block body
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* @param {ASTNode} node The node to check
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* @param {ASTNode[]} statements collection of ASTNodes for the parent node block
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* @returns {boolean} True if var is on top otherwise false
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*/
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function isVarOnTop(node, statements) {
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const l = statements.length;
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let i = 0;
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// skip over directives
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for (; i < l; ++i) {
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if (!looksLikeDirective(statements[i]) && !looksLikeImport(statements[i])) {
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break;
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}
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}
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for (; i < l; ++i) {
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if (!isVariableDeclaration(statements[i])) {
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return false;
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}
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if (statements[i] === node) {
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return true;
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}
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}
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return false;
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}
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/**
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* Checks whether variable is on top at the global level
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* @param {ASTNode} node The node to check
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* @param {ASTNode} parent Parent of the node
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* @returns {void}
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*/
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function globalVarCheck(node, parent) {
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if (!isVarOnTop(node, parent.body)) {
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context.report({ node, messageId: "top" });
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}
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}
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/**
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* Checks whether variable is on top at functional block scope level
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* @param {ASTNode} node The node to check
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* @param {ASTNode} parent Parent of the node
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* @param {ASTNode} grandParent Parent of the node's parent
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* @returns {void}
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*/
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function blockScopeVarCheck(node, parent, grandParent) {
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if (!(/Function/u.test(grandParent.type) &&
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parent.type === "BlockStatement" &&
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isVarOnTop(node, parent.body))) {
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context.report({ node, messageId: "top" });
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}
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}
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//--------------------------------------------------------------------------
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// Public API
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//--------------------------------------------------------------------------
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return {
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"VariableDeclaration[kind='var']"(node) {
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if (node.parent.type === "ExportNamedDeclaration") {
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globalVarCheck(node.parent, node.parent.parent);
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} else if (node.parent.type === "Program") {
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globalVarCheck(node, node.parent);
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} else {
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blockScopeVarCheck(node, node.parent, node.parent.parent);
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}
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}
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};
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}
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};
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