2 * @fileoverview Rule to flag on declaring variables already declared in the outer scope
8 //------------------------------------------------------------------------------
10 //------------------------------------------------------------------------------
12 const astUtils = require("./utils/ast-utils");
14 //------------------------------------------------------------------------------
16 //------------------------------------------------------------------------------
23 description: "disallow variable declarations from shadowing variables declared in the outer scope",
24 category: "Variables",
26 url: "https://eslint.org/docs/rules/no-shadow"
33 builtinGlobals: { type: "boolean", default: false },
34 hoist: { enum: ["all", "functions", "never"], default: "functions" },
42 additionalProperties: false
50 builtinGlobals: context.options[0] && context.options[0].builtinGlobals,
51 hoist: (context.options[0] && context.options[0].hoist) || "functions",
52 allow: (context.options[0] && context.options[0].allow) || []
56 * Check if variable name is allowed.
57 * @param {ASTNode} variable The variable to check.
58 * @returns {boolean} Whether or not the variable name is allowed.
60 function isAllowed(variable) {
61 return options.allow.indexOf(variable.name) !== -1;
65 * Checks if a variable of the class name in the class scope of ClassDeclaration.
67 * ClassDeclaration creates two variables of its name into its outer scope and its class scope.
68 * So we should ignore the variable in the class scope.
69 * @param {Object} variable The variable to check.
70 * @returns {boolean} Whether or not the variable of the class name in the class scope of ClassDeclaration.
72 function isDuplicatedClassNameVariable(variable) {
73 const block = variable.scope.block;
75 return block.type === "ClassDeclaration" && block.id === variable.identifiers[0];
79 * Checks if a variable is inside the initializer of scopeVar.
81 * To avoid reporting at declarations such as `var a = function a() {};`.
82 * But it should report `var a = function(a) {};` or `var a = function() { function a() {} };`.
83 * @param {Object} variable The variable to check.
84 * @param {Object} scopeVar The scope variable to look for.
85 * @returns {boolean} Whether or not the variable is inside initializer of scopeVar.
87 function isOnInitializer(variable, scopeVar) {
88 const outerScope = scopeVar.scope;
89 const outerDef = scopeVar.defs[0];
90 const outer = outerDef && outerDef.parent && outerDef.parent.range;
91 const innerScope = variable.scope;
92 const innerDef = variable.defs[0];
93 const inner = innerDef && innerDef.name.range;
98 outer[0] < inner[0] &&
99 inner[1] < outer[1] &&
100 ((innerDef.type === "FunctionName" && innerDef.node.type === "FunctionExpression") || innerDef.node.type === "ClassExpression") &&
101 outerScope === innerScope.upper
106 * Get a range of a variable's identifier node.
107 * @param {Object} variable The variable to get.
108 * @returns {Array|undefined} The range of the variable's identifier node.
110 function getNameRange(variable) {
111 const def = variable.defs[0];
113 return def && def.name.range;
117 * Checks if a variable is in TDZ of scopeVar.
118 * @param {Object} variable The variable to check.
119 * @param {Object} scopeVar The variable of TDZ.
120 * @returns {boolean} Whether or not the variable is in TDZ of scopeVar.
122 function isInTdz(variable, scopeVar) {
123 const outerDef = scopeVar.defs[0];
124 const inner = getNameRange(variable);
125 const outer = getNameRange(scopeVar);
130 inner[1] < outer[0] &&
132 // Excepts FunctionDeclaration if is {"hoist":"function"}.
133 (options.hoist !== "functions" || !outerDef || outerDef.node.type !== "FunctionDeclaration")
138 * Checks the current context for shadowed variables.
139 * @param {Scope} scope Fixme
142 function checkForShadows(scope) {
143 const variables = scope.variables;
145 for (let i = 0; i < variables.length; ++i) {
146 const variable = variables[i];
148 // Skips "arguments" or variables of a class name in the class scope of ClassDeclaration.
149 if (variable.identifiers.length === 0 ||
150 isDuplicatedClassNameVariable(variable) ||
156 // Gets shadowed variable.
157 const shadowed = astUtils.getVariableByName(scope.upper, variable.name);
160 (shadowed.identifiers.length > 0 || (options.builtinGlobals && "writeable" in shadowed)) &&
161 !isOnInitializer(variable, shadowed) &&
162 !(options.hoist !== "all" && isInTdz(variable, shadowed))
165 node: variable.identifiers[0],
166 message: "'{{name}}' is already declared in the upper scope.",
175 const globalScope = context.getScope();
176 const stack = globalScope.childScopes.slice();
178 while (stack.length) {
179 const scope = stack.pop();
181 stack.push(...scope.childScopes);
182 checkForShadows(scope);