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