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app_vue/node_modules/eslint/lib/rules/no-var.js

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+/**
+ * @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
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "suggestion",
+
+        docs: {
+            description: "require `let` or `const` instead of `var`",
+            category: "ECMAScript 6",
+            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);
+                }
+            }
+        };
+    }
+};