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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);
}
}
};
}
};
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