Current File : /var/www/html/node_modules/eslint/lib/rules/no-var.js
/**
* @fileoverview Rule to check for the usage of var.
* @author Jamund Ferguson
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
const astUtils = require("./utils/ast-utils");
//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------
/**
* Check whether a given variable is a global variable or not.
* @param {eslint-scope.Variable} variable The variable to check.
* @returns {boolean} `true` if the variable is a global variable.
*/
function isGlobal(variable) {
return Boolean(variable.scope) && variable.scope.type === "global";
}
/**
* Finds the nearest function scope or global scope walking up the scope
* hierarchy.
* @param {eslint-scope.Scope} scope The scope to traverse.
* @returns {eslint-scope.Scope} a function scope or global scope containing the given
* scope.
*/
function getEnclosingFunctionScope(scope) {
let currentScope = scope;
while (currentScope.type !== "function" && currentScope.type !== "global") {
currentScope = currentScope.upper;
}
return currentScope;
}
/**
* Checks whether the given variable has any references from a more specific
* function expression (i.e. a closure).
* @param {eslint-scope.Variable} variable A variable to check.
* @returns {boolean} `true` if the variable is used from a closure.
*/
function isReferencedInClosure(variable) {
const enclosingFunctionScope = getEnclosingFunctionScope(variable.scope);
return variable.references.some(reference =>
getEnclosingFunctionScope(reference.from) !== enclosingFunctionScope);
}
/**
* Checks whether the given node is the assignee of a loop.
* @param {ASTNode} node A VariableDeclaration node to check.
* @returns {boolean} `true` if the declaration is assigned as part of loop
* iteration.
*/
function isLoopAssignee(node) {
return (node.parent.type === "ForOfStatement" || node.parent.type === "ForInStatement") &&
node === node.parent.left;
}
/**
* Checks whether the given variable declaration is immediately initialized.
* @param {ASTNode} node A VariableDeclaration node to check.
* @returns {boolean} `true` if the declaration has an initializer.
*/
function isDeclarationInitialized(node) {
return node.declarations.every(declarator => declarator.init !== null);
}
const SCOPE_NODE_TYPE = /^(?:Program|BlockStatement|SwitchStatement|ForStatement|ForInStatement|ForOfStatement)$/u;
/**
* Gets the scope node which directly contains a given node.
* @param {ASTNode} node A node to get. This is a `VariableDeclaration` or
* an `Identifier`.
* @returns {ASTNode} A scope node. This is one of `Program`, `BlockStatement`,
* `SwitchStatement`, `ForStatement`, `ForInStatement`, and
* `ForOfStatement`.
*/
function getScopeNode(node) {
for (let currentNode = node; currentNode; currentNode = currentNode.parent) {
if (SCOPE_NODE_TYPE.test(currentNode.type)) {
return currentNode;
}
}
/* istanbul ignore next : unreachable */
return null;
}
/**
* Checks whether a given variable is redeclared or not.
* @param {eslint-scope.Variable} variable A variable to check.
* @returns {boolean} `true` if the variable is redeclared.
*/
function isRedeclared(variable) {
return variable.defs.length >= 2;
}
/**
* Checks whether a given variable is used from outside of the specified scope.
* @param {ASTNode} scopeNode A scope node to check.
* @returns {Function} The predicate function which checks whether a given
* variable is used from outside of the specified scope.
*/
function isUsedFromOutsideOf(scopeNode) {
/**
* Checks whether a given reference is inside of the specified scope or not.
* @param {eslint-scope.Reference} reference A reference to check.
* @returns {boolean} `true` if the reference is inside of the specified
* scope.
*/
function isOutsideOfScope(reference) {
const scope = scopeNode.range;
const id = reference.identifier.range;
return id[0] < scope[0] || id[1] > scope[1];
}
return function(variable) {
return variable.references.some(isOutsideOfScope);
};
}
/**
* Creates the predicate function which checks whether a variable has their references in TDZ.
*
* The predicate function would return `true`:
*
* - if a reference is before the declarator. E.g. (var a = b, b = 1;)(var {a = b, b} = {};)
* - if a reference is in the expression of their default value. E.g. (var {a = a} = {};)
* - if a reference is in the expression of their initializer. E.g. (var a = a;)
* @param {ASTNode} node The initializer node of VariableDeclarator.
* @returns {Function} The predicate function.
* @private
*/
function hasReferenceInTDZ(node) {
const initStart = node.range[0];
const initEnd = node.range[1];
return variable => {
const id = variable.defs[0].name;
const idStart = id.range[0];
const defaultValue = (id.parent.type === "AssignmentPattern" ? id.parent.right : null);
const defaultStart = defaultValue && defaultValue.range[0];
const defaultEnd = defaultValue && defaultValue.range[1];
return variable.references.some(reference => {
const start = reference.identifier.range[0];
const end = reference.identifier.range[1];
return !reference.init && (
start < idStart ||
(defaultValue !== null && start >= defaultStart && end <= defaultEnd) ||
(start >= initStart && end <= initEnd)
);
});
};
}
/**
* Checks whether a given variable has name that is allowed for 'var' declarations,
* but disallowed for `let` declarations.
* @param {eslint-scope.Variable} variable The variable to check.
* @returns {boolean} `true` if the variable has a disallowed name.
*/
function hasNameDisallowedForLetDeclarations(variable) {
return variable.name === "let";
}
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/** @type {import('../shared/types').Rule} */
module.exports = {
meta: {
type: "suggestion",
docs: {
description: "require `let` or `const` instead of `var`",
recommended: false,
url: "https://eslint.org/docs/rules/no-var"
},
schema: [],
fixable: "code",
messages: {
unexpectedVar: "Unexpected var, use let or const instead."
}
},
create(context) {
const sourceCode = context.getSourceCode();
/**
* Checks whether the variables which are defined by the given declarator node have their references in TDZ.
* @param {ASTNode} declarator The VariableDeclarator node to check.
* @returns {boolean} `true` if one of the variables which are defined by the given declarator node have their references in TDZ.
*/
function hasSelfReferenceInTDZ(declarator) {
if (!declarator.init) {
return false;
}
const variables = context.getDeclaredVariables(declarator);
return variables.some(hasReferenceInTDZ(declarator.init));
}
/**
* Checks whether it can fix a given variable declaration or not.
* It cannot fix if the following cases:
*
* - A variable is a global variable.
* - A variable is declared on a SwitchCase node.
* - A variable is redeclared.
* - A variable is used from outside the scope.
* - A variable is used from a closure within a loop.
* - A variable might be used before it is assigned within a loop.
* - A variable might be used in TDZ.
* - A variable is declared in statement position (e.g. a single-line `IfStatement`)
* - A variable has name that is disallowed for `let` declarations.
*
* ## A variable is declared on a SwitchCase node.
*
* If this rule modifies 'var' declarations on a SwitchCase node, it
* would generate the warnings of 'no-case-declarations' rule. And the
* 'eslint:recommended' preset includes 'no-case-declarations' rule, so
* this rule doesn't modify those declarations.
*
* ## A variable is redeclared.
*
* The language spec disallows redeclarations of `let` declarations.
* Those variables would cause syntax errors.
*
* ## A variable is used from outside the scope.
*
* The language spec disallows accesses from outside of the scope for
* `let` declarations. Those variables would cause reference errors.
*
* ## A variable is used from a closure within a loop.
*
* A `var` declaration within a loop shares the same variable instance
* across all loop iterations, while a `let` declaration creates a new
* instance for each iteration. This means if a variable in a loop is
* referenced by any closure, changing it from `var` to `let` would
* change the behavior in a way that is generally unsafe.
*
* ## A variable might be used before it is assigned within a loop.
*
* Within a loop, a `let` declaration without an initializer will be
* initialized to null, while a `var` declaration will retain its value
* from the previous iteration, so it is only safe to change `var` to
* `let` if we can statically determine that the variable is always
* assigned a value before its first access in the loop body. To keep
* the implementation simple, we only convert `var` to `let` within
* loops when the variable is a loop assignee or the declaration has an
* initializer.
* @param {ASTNode} node A variable declaration node to check.
* @returns {boolean} `true` if it can fix the node.
*/
function canFix(node) {
const variables = context.getDeclaredVariables(node);
const scopeNode = getScopeNode(node);
if (node.parent.type === "SwitchCase" ||
node.declarations.some(hasSelfReferenceInTDZ) ||
variables.some(isGlobal) ||
variables.some(isRedeclared) ||
variables.some(isUsedFromOutsideOf(scopeNode)) ||
variables.some(hasNameDisallowedForLetDeclarations)
) {
return false;
}
if (astUtils.isInLoop(node)) {
if (variables.some(isReferencedInClosure)) {
return false;
}
if (!isLoopAssignee(node) && !isDeclarationInitialized(node)) {
return false;
}
}
if (
!isLoopAssignee(node) &&
!(node.parent.type === "ForStatement" && node.parent.init === node) &&
!astUtils.STATEMENT_LIST_PARENTS.has(node.parent.type)
) {
// If the declaration is not in a block, e.g. `if (foo) var bar = 1;`, then it can't be fixed.
return false;
}
return true;
}
/**
* Reports a given variable declaration node.
* @param {ASTNode} node A variable declaration node to report.
* @returns {void}
*/
function report(node) {
context.report({
node,
messageId: "unexpectedVar",
fix(fixer) {
const varToken = sourceCode.getFirstToken(node, { filter: t => t.value === "var" });
return canFix(node)
? fixer.replaceText(varToken, "let")
: null;
}
});
}
return {
"VariableDeclaration:exit"(node) {
if (node.kind === "var") {
report(node);
}
}
};
}
};
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