Current File : /var/www/html/node_modules/eslint/lib/rules/no-use-before-define.js
/**
* @fileoverview Rule to flag use of variables before they are defined
* @author Ilya Volodin
*/
"use strict";
//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------
const SENTINEL_TYPE = /^(?:(?:Function|Class)(?:Declaration|Expression)|ArrowFunctionExpression|CatchClause|ImportDeclaration|ExportNamedDeclaration)$/u;
const FOR_IN_OF_TYPE = /^For(?:In|Of)Statement$/u;
/**
* Parses a given value as options.
* @param {any} options A value to parse.
* @returns {Object} The parsed options.
*/
function parseOptions(options) {
let functions = true;
let classes = true;
let variables = true;
if (typeof options === "string") {
functions = (options !== "nofunc");
} else if (typeof options === "object" && options !== null) {
functions = options.functions !== false;
classes = options.classes !== false;
variables = options.variables !== false;
}
return { functions, classes, variables };
}
/**
* Checks whether or not a given location is inside of the range of a given node.
* @param {ASTNode} node An node to check.
* @param {number} location A location to check.
* @returns {boolean} `true` if the location is inside of the range of the node.
*/
function isInRange(node, location) {
return node && node.range[0] <= location && location <= node.range[1];
}
/**
* Checks whether or not a given location is inside of the range of a class static initializer.
* Static initializers are static blocks and initializers of static fields.
* @param {ASTNode} node `ClassBody` node to check static initializers.
* @param {number} location A location to check.
* @returns {boolean} `true` if the location is inside of a class static initializer.
*/
function isInClassStaticInitializerRange(node, location) {
return node.body.some(classMember => (
(
classMember.type === "StaticBlock" &&
isInRange(classMember, location)
) ||
(
classMember.type === "PropertyDefinition" &&
classMember.static &&
classMember.value &&
isInRange(classMember.value, location)
)
));
}
/**
* Checks whether a given scope is the scope of a a class static initializer.
* Static initializers are static blocks and initializers of static fields.
* @param {eslint-scope.Scope} scope A scope to check.
* @returns {boolean} `true` if the scope is a class static initializer scope.
*/
function isClassStaticInitializerScope(scope) {
if (scope.type === "class-static-block") {
return true;
}
if (scope.type === "class-field-initializer") {
// `scope.block` is PropertyDefinition#value node
const propertyDefinition = scope.block.parent;
return propertyDefinition.static;
}
return false;
}
/**
* Checks whether a given reference is evaluated in an execution context
* that isn't the one where the variable it refers to is defined.
* Execution contexts are:
* - top-level
* - functions
* - class field initializers (implicit functions)
* - class static blocks (implicit functions)
* Static class field initializers and class static blocks are automatically run during the class definition evaluation,
* and therefore we'll consider them as a part of the parent execution context.
* Example:
*
* const x = 1;
*
* x; // returns `false`
* () => x; // returns `true`
*
* class C {
* field = x; // returns `true`
* static field = x; // returns `false`
*
* method() {
* x; // returns `true`
* }
*
* static method() {
* x; // returns `true`
* }
*
* static {
* x; // returns `false`
* }
* }
* @param {eslint-scope.Reference} reference A reference to check.
* @returns {boolean} `true` if the reference is from a separate execution context.
*/
function isFromSeparateExecutionContext(reference) {
const variable = reference.resolved;
let scope = reference.from;
// Scope#variableScope represents execution context
while (variable.scope.variableScope !== scope.variableScope) {
if (isClassStaticInitializerScope(scope.variableScope)) {
scope = scope.variableScope.upper;
} else {
return true;
}
}
return false;
}
/**
* Checks whether or not a given reference is evaluated during the initialization of its variable.
*
* This returns `true` in the following cases:
*
* var a = a
* var [a = a] = list
* var {a = a} = obj
* for (var a in a) {}
* for (var a of a) {}
* var C = class { [C]; };
* var C = class { static foo = C; };
* var C = class { static { foo = C; } };
* class C extends C {}
* class C extends (class { static foo = C; }) {}
* class C { [C]; }
* @param {Reference} reference A reference to check.
* @returns {boolean} `true` if the reference is evaluated during the initialization.
*/
function isEvaluatedDuringInitialization(reference) {
if (isFromSeparateExecutionContext(reference)) {
/*
* Even if the reference appears in the initializer, it isn't evaluated during the initialization.
* For example, `const x = () => x;` is valid.
*/
return false;
}
const location = reference.identifier.range[1];
const definition = reference.resolved.defs[0];
if (definition.type === "ClassName") {
// `ClassDeclaration` or `ClassExpression`
const classDefinition = definition.node;
return (
isInRange(classDefinition, location) &&
/*
* Class binding is initialized before running static initializers.
* For example, `class C { static foo = C; static { bar = C; } }` is valid.
*/
!isInClassStaticInitializerRange(classDefinition.body, location)
);
}
let node = definition.name.parent;
while (node) {
if (node.type === "VariableDeclarator") {
if (isInRange(node.init, location)) {
return true;
}
if (FOR_IN_OF_TYPE.test(node.parent.parent.type) &&
isInRange(node.parent.parent.right, location)
) {
return true;
}
break;
} else if (node.type === "AssignmentPattern") {
if (isInRange(node.right, location)) {
return true;
}
} else if (SENTINEL_TYPE.test(node.type)) {
break;
}
node = node.parent;
}
return false;
}
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/** @type {import('../shared/types').Rule} */
module.exports = {
meta: {
type: "problem",
docs: {
description: "disallow the use of variables before they are defined",
recommended: false,
url: "https://eslint.org/docs/rules/no-use-before-define"
},
schema: [
{
oneOf: [
{
enum: ["nofunc"]
},
{
type: "object",
properties: {
functions: { type: "boolean" },
classes: { type: "boolean" },
variables: { type: "boolean" }
},
additionalProperties: false
}
]
}
],
messages: {
usedBeforeDefined: "'{{name}}' was used before it was defined."
}
},
create(context) {
const options = parseOptions(context.options[0]);
/**
* Determines whether a given reference should be checked.
*
* Returns `false` if the reference is:
* - initialization's (e.g., `let a = 1`).
* - referring to an undefined variable (i.e., if it's an unresolved reference).
* - referring to a variable that is defined, but not in the given source code
* (e.g., global environment variable or `arguments` in functions).
* - allowed by options.
* @param {eslint-scope.Reference} reference The reference
* @returns {boolean} `true` if the reference should be checked
*/
function shouldCheck(reference) {
if (reference.init) {
return false;
}
const variable = reference.resolved;
if (!variable || variable.defs.length === 0) {
return false;
}
const definitionType = variable.defs[0].type;
if (!options.functions && definitionType === "FunctionName") {
return false;
}
if (
(
!options.variables && definitionType === "Variable" ||
!options.classes && definitionType === "ClassName"
) &&
// don't skip checking the reference if it's in the same execution context, because of TDZ
isFromSeparateExecutionContext(reference)
) {
return false;
}
return true;
}
/**
* Finds and validates all references in a given scope and its child scopes.
* @param {eslint-scope.Scope} scope The scope object.
* @returns {void}
*/
function checkReferencesInScope(scope) {
scope.references.filter(shouldCheck).forEach(reference => {
const variable = reference.resolved;
const definitionIdentifier = variable.defs[0].name;
if (
reference.identifier.range[1] < definitionIdentifier.range[1] ||
isEvaluatedDuringInitialization(reference)
) {
context.report({
node: reference.identifier,
messageId: "usedBeforeDefined",
data: reference.identifier
});
}
});
scope.childScopes.forEach(checkReferencesInScope);
}
return {
Program() {
checkReferencesInScope(context.getScope());
}
};
}
};
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