Error codes

quick-lint-js can find the following warnings and errors in your code:

• E0001: variable assigned before its declaration
• E0002: assignment to const global variable
• E0003: cannot assign to const variable
• E0004: assignment to const variable before its declaration
• E0005: BigInt literal contains decimal point
• E0006: BigInt literal contains exponent
• E0007: classes cannot be named 'let'
• E0008: let statement cannot declare variables named 'let'
• E0009: cannot export variable named 'let'
• E0010: cannot import 'let'
• E0011: character is not allowed in identifiers
• E0012: escaped character is not allowed in identifiers
• E0013: code point out of range
• E0014: expected expression before newline
• E0015: expected expression before semicolon
• E0016: expected hexadecimal digits in Unicode escape sequence
• E0017: if statement needs parentheses around condition
• E0018: if statement is missing '(' or ')' around condition
• E0019: escaping '-' is not allowed in tag names; write '-' instead
• E0020: invalid expression left of assignment
• E0021: invalid lone literal in object literal
• E0022: invalid UTF-8 sequence
• E0023: keywords cannot contain escape sequences
• E0024: const/let/var with no bindings
• E0025: missing comma between object literal entries
• E0026: missing operand for operator
• E0027: missing semicolon after statement
• E0028: number literal contains consecutive underscores
• E0029: number literal contains trailing underscores
• E0030: octal literal may not have exponent
• E0031: octal literal may not have decimal
• E0032: legacy octal literal may not be BigInt
• E0033: redeclaration of global variable
• E0034: redeclaration of variable
• E0035: RegExp literal flags cannot contain Unicode escapes
• E0036: stray comma in let statement
• E0037: unclosed block comment
• E0038: unclosed identifier escape sequence
• E0039: unclosed regexp literal
• E0040: unclosed string literal
• E0041: unclosed template
• E0042: unexpected '@'
• E0043: unexpected '\' in identifier
• E0044: unexpected characters in number literal
• E0045: unexpected control character
• E0046: unexpected characters in binary literal
• E0047: unexpected characters in octal literal
• E0048: unexpected characters in hex literal
• E0049: binary number literal has no digits
• E0050: hex number literal has no digits
• E0051: octal number literal has no digits
• E0052: unexpected '#'
• E0053: missing property name between '.' and '.'
• E0054: unexpected token
• E0055: unmatched indexing bracket
• E0056: unmatched parenthesis
• E0057: use of undeclared variable
• E0058: variable used before declaration
• E0059: assignment to undeclared variable
• E0060: invalid hex escape sequence
• E0061: missing name in function statement
• E0062: missing name or parentheses for function
• E0063: missing operator between expression and arrow function
• E0064: missing body for 'if' statement
• E0065: 'else' has no corresponding 'if'
• E0066: exporting requires '{' and '}'
• E0067: exporting requires 'default'
• E0068: extra ',' is not allowed between function call arguments
• E0069: cannot declare 'await' inside async function
• E0070: commas are not allowed after spread parameter
• E0071: cannot declare 'yield' inside generator function
• E0072: methods should not use the 'function' keyword
• E0073: missing function parameter list
• E0074: '.' operator needs a key name; use + to concatenate strings; use [] to access with a dynamic key
• E0075: indexing requires an expression
• E0076: cannot declare and export variable with 'export default'
• E0077: function call before declaration in blocked scope
• E0078: missing expression between parentheses
• E0079: missing name of exported function
• E0080: missing name of class
• E0081: missing name of exported class
• E0082: assigning to 'async' in a for-of loop requires parentheses
• E0083: missing value for object property
• E0084: do-while loop needs parentheses around condition
• E0085: do-while loop is missing '(' or ')' around condition
• E0086: redundant delete statement on variable
• E0087: while loop needs parentheses around condition
• E0088: while loop is missing '(' or ')' around condition
• E0089: with statement needs parentheses around expression
• E0090: with statement is missing '(' or ')' around expression
• E0091: switch statement needs parentheses around condition
• E0092: switch statement is missing '(' or ')' around condition
• E0093: C-style for loop is missing its third component
• E0094: missing body for 'for' loop
• E0095: Unicode byte order mark (BOM) cannot appear before #! at beginning of script
• E0096: missing for loop header
• E0097: for loop needs an iterable, or condition and update clauses
• E0098: for loop needs an iterable, or condition and update clauses
• E0099: missing semicolon between init and condition parts of for loop
• E0100: missing semicolon between condition and update parts of for loop
• E0101: missing body for do-while loop
• E0102: C-style for loops have only three semicolon-separated components
• E0103: missing 'while (condition)' for do-while statement
• E0104: missing body for while loop
• E0105: missing parameters for arrow function
• E0106: missing body for 'switch' statement
• E0107: expected '{'
• E0108: 'in' disallowed in C-style for loop initializer
• E0109: for-of loop expression cannot have semicolons
• E0110: for-in loop expression cannot have semicolons
• E0111: missing body for class
• E0112: unexpected token in export; expected 'export default ...' or 'export {name}' or 'export * from ...' or 'export class' or 'export function' or 'export let'
• E0113: incomplete export; expected 'export default ...' or 'export {name}' or 'export * from ...' or 'export class' or 'export function' or 'export let'
• E0114: unexpected token in variable declaration; expected variable name
• E0115: unexpected 'case' outside switch statement
• E0116: unexpected 'default' outside switch statement
• E0117: unexpected 'catch' without 'try'
• E0118: unexpected 'finally' without 'try'
• E0119: missing body for catch clause
• E0120: missing body for try statement
• E0121: missing body for finally clause
• E0122: missing catch or finally clause for try statement
• E0123: missing variable name
• E0124: cannot declare variable named keyword
• E0125: missing header and body for 'for' loop
• E0126: expected 'as' between '*' and variable
• E0127: TypeScript's 'enum' feature is not allowed in JavaScript
• E0128: expected 'from' before module specifier
• E0129: expected 'from "name_of_module.mjs"'
• E0130: missing catch variable name between parentheses
• E0131: expected ',' between object literal entries
• E0132: missing ',' between variable declarations
• E0133: error generator function star belongs before name
• E0134: unclosed code block; expected '}' by end of file
• E0135: expected variable name for 'catch'
• E0136: cannot update variable with '+=' while declaring it
• E0137: missing condition for switch statement
• E0138: missing condition for if statement
• E0139: missing condition for while statement
• E0140: expected expression after 'case'
• E0141: expected ')' to close function call
• E0142: missing property name after '.' operator
• E0143: unmatched '}'
• E0144: cannot export variable named keyword
• E0145: cannot import variable named keyword
• E0146: missing ':' in conditional expression
• E0147: unexpected identifier in expression; missing operator before
• E0148: missing body for statement; a function statement is not allowed as the body of statement
• E0149: missing body for statement; a class statement is not allowed as the body of statement
• E0150: missing body for statement; a lexical declaration is not allowed as the body of statement
• E0151: invalid function parameter
• E0152: legacy octal literals may not contain underscores
• E0153: forwarding exports are only allowed in export-from
• E0154: unexpected expression; missing key for object entry
• E0155: cannot reference private variables without object; use 'this.'
• E0156: private properties are not allowed in object literals
• E0157: missing end of array; expected ']'
• E0158: unexpected '=>'; expected parameter for arrow function, but got a literal instead
• E0159: unexpected literal in parameter list; expected parameter name
• E0160: unexpected '=>'; expected parameter for arrow function, but got an expression instead
• E0161: unclosed object literal; expected '}'
• E0162: 'await' is only allowed in async functions
• E0163: newline is not allowed between 'async' and arrow function parameter list
• E0164: JSON syntax error
• E0165: TypeScript style const field
• E0166: "globals" descriptor "shadowable" property must be a boolean
• E0167: "globals" descriptor "writable" property must be a boolean
• E0168: "globals" must be an object
• E0169: "global-groups" must be a boolean or an array
• E0170: "global-groups" entries must be strings
• E0171: "globals" descriptor must be a boolean or an object
• E0172: missing body for function
• E0173: cannot assign to loop variable in for of/in loop
• E0174: functions/methods should not have '=>'
• E0175: expected variable name for 'import'-'as'
• E0176: missing arrow operator for arrow function
• E0177: React/JSX is not allowed in vanilla JavaScript code
• E0178: 'await' cannot be followed by an arrow function; use 'async' instead
• E0179: return statement returns nothing (undefined)
• E0180: stray comma in function parameter
• E0181: unclosed string literal
• E0182: '>' is not allowed directly in JSX text; write {'>'} or > instead
• E0183: '}' is not allowed directly in JSX text; write {'}'} instead
• E0184: missing 'if' after 'else'
• E0185: assignment to imported variable; imported variable declared here
• E0186: missing '...' in JSX attribute spread
• E0187: mismatched JSX tags; expected </foo>
• E0188: '=' changes variables; to compare, use '===' instead
• E0189: missing '<>' and '</>' to enclose multiple children
• E0190: missing comparison; '===' does not extend to the right side of '||'
• E0191: event attributes must be camelCase
• E0192: attribute has wrong capitalization
• E0193: misspelled React attribute; write 'className' instead
• E0194: missing parentheses around left-hand side of **; ** operator cannot be used after unary - without parentheses
• E0195: missing parentheses around operand of typeof; typeof operator cannot be used before ** without parentheses
• E0196: new variable shadows existing variable
• E0197: '“' is not allowed for strings; use " instead
• E0198: unexpected statement before first switch case, expected 'case' or 'default'
• E0199: unclosed class; expected '}' by end of file
• E0200: break can only be used inside of a loop or switch
• E0201: continue can only be used inside of a loop
• E0202: missing '=' after variable
• E0203: depth limit exceeded
• E0204: error generator function star belongs after keyword function
• E0205: error missing initializer in const declaration
• E0206: label named 'await' not allowed in async function
• E0207: code point in Unicode escape sequence must not be greater than U+10FFFF
• E0208: cannot access private identifier outside class
• E0209: commas are not allowed between class methods
• E0210: unopened block comment
• E0211: missing parentheses around self-invoked function
• E0212: integer cannot be represented and will be rounded
• E0213: TypeScript's 'interface' feature is not allowed in JavaScript code
• E0214: use of undeclared type
• E0215: unclosed interface; expected '}' by end of file
• E0216: TypeScript interface properties cannot be 'static'
• E0217: TypeScript interface methods cannot be marked 'async'
• E0218: TypeScript interface methods cannot be marked as a generator
• E0219: interface properties are always public and cannot be private
• E0220: TypeScript interface methods cannot contain a body
• E0221: TypeScript interface fields cannot be initalized
• E0222: 'private' is not allowed in JavaScript
• E0223: missing semicolon after field
• E0224: TypeScript type annotations are not allowed in JavaScript code
• E0225: index signatures require a value type
• E0226: missing semicolon after index signature
• E0227: index signature must be a field, not a method
• E0228: TypeScript optional properties are not allowed in JavaScript code
• E0229: missing name for class method
• E0230: TypeScript's 'readonly' feature is not allowed in JavaScript code
• E0231: methods cannot be readonly
• E0232: 'readonly static' is not allowed; write 'static readonly' instead
• E0233: TypeScript generics are not allowed in JavaScript code
• E0234: 'protected' is not allowed in JavaScript
• E0235: missing quotes around module name
• E0236: assignment-asserted field must have a type annotation
• E0237: interface properties cannot be marked public explicitly
• E0238: assignment-asserted fields are not supported in interfaces
• E0239: TypeScript assignment-asserted fields are not supported in JavaScript
• E0240: '!' is not allowed on methods
• E0241: newline is not allowed between field name and '!'
• E0243: interfaces cannot contain static blocks
• E0244: abstract classes are not allowed in JavaScript
• E0245: missing body for TypeScript interface
• E0246: 'extends' must be before 'implements'
• E0247: TypeScript 'implements' is not allowed in JavaScript
• E0248: extra ',' is not allowed between enum members
• E0249: computed enum member name must be a simple string
• E0250: enum member name cannot be numeric
• E0251: enum value must be a compile-time constant
• E0252: enum member needs initializer; computed value disables enum autoincrement
• E0253: use ':' instead of '=' in object literals
• E0254: unexpected ':' in expression; did you mean 'as'?
• E0255: missing parentheses around parameter; TypeScript type annotation requires parentheses
• E0256: catch variable can only be typed as '*', 'any', or 'unknown'
• E0257: missing ',', ';', or newline between object type entries
• E0258: missing type between '|' and '|' (or '&' and '&')
• E0259: '.' is not allowed after generic arguments
• E0260: TypeScript non-null assertion is not allowed on parameters
• E0261: TypeScript non-null assertions are not allowed in JavaScript
• E0262: leading commas are not allowed in generic parameter lists
• E0263: only one comma is allowed between or after generic parameters
• E0264: expected at least one parameter in generic parameter list
• E0265: missing comma between generic parameters
• E0266: redundant 'await'
• E0267: TypeScript types are not allowed in JavaScript
• E0268: TypeScript type imports cannot import both default and named exports
• E0269: 'async static' is not allowed; write 'static async' instead
• E0270: TypeScript type imports are not allowed in JavaScript
• E0271: TypeScript type imports are not allowed in JavaScript
• E0272: 'type' cannot be used twice in import
• E0273: TypeScript namespaces are not allowed in JavaScript
• E0274: TypeScript import aliases are not allowed in JavaScript
• E0275: newline is not allowed after 'interface'
• E0276: newline is not allowed after 'namespace'
• E0277: newline is not allowed after 'type'
• E0278: TypeScript type exports are not allowed in JavaScript
• E0279: TypeScript type exports are not allowed in JavaScript
• E0280: 'type' cannot be used twice in export
• E0281: TypeScript 'as' type assertions are not allowed in JavaScript
• E0282: use ':' instead of 'as' to type a function parameter
• E0283: TypeScript <Type> casts are not allowed in JSX mode
• E0284: missing TypeScript type
• E0285: generic arrow function needs ',' here in TSX
• E0286: lower case letters compared with toUpperCase
• E0287: upper case letters compared with toLowerCase
• E0288: TypeScript interface properties are always public and cannot be marked protected
• E0289: 'public' is not allowed in JavaScript
• E0290: assignment-assertion fields cannot have default values
• E0291: 'as const' is only allowed on literals (array, object, string, boolean) and enum members
• E0292: missing semicolon after interface method
• E0293: missing semicolon after abstract method
• E0294: abstract methods cannot contain a body
• E0295: abstract fields cannot have default values
• E0296: abstract properties are only allowed in abstract classes
• E0297: abstract properties are not allowed in interfaces
• E0298: abstract methods cannot be marked 'async'
• E0299: abstract methods cannot be marked as a generator
• E0300: newline is not allowed after 'abstract'
• E0301: 'this' parameters are not allowed in arrow functions
• E0302: 'this' parameter not allowed when destructuring
• E0303: 'this' must be the first parameter
• E0304: cannot use '...' on 'this' parameter
• E0305: 'this' parameters are not allowed in JavaScript
• E0306: React/JSX is not allowed in vanilla TypeScript code
• E0307: unexpected '?'
• E0308: TypeScript optional parameters are not allowed in JavaScript
• E0309: unexpected '?' when destructuring
• E0310: optional parameter cannot have both '?' and initializer; remove '?'
• E0311: missing parentheses around parameter; TypeScript optional parameter requires parentheses
• E0312: missing parentheses around parameter; TypeScript optional parameter with type annotation requires parentheses
• E0313: 'readonly' only works with array types and tuple types
• E0315: (name) is not the name of a parameter
• E0316: function overload signature must be named (function name)
• E0317: newline is not allowed between 'async' and 'function'
• E0318: function overload signature cannot have generator '*'
• E0319: missing name for element in named tuple type
• E0320: missing name for element in named tuple type
• E0321: expected '?' to mark tuple element as optional
• E0323: optional tuple elements cannot come after spread elements
• E0324: spread tuple elements cannot be optional
• E0325: cannot delete variables in TypeScript
• E0326: 'async export' is not allowed; write 'export async' instead
• E0327: 'function async' is not allowed; write 'async function' instead
• E0341: using '===' or '!==' against an array literal does not compare items
• E0342: using equality or inequality operators against an arrow function will always produce the same result
• E0343: using '==' against a class literal always returns 'false'
• E0344: using '===' or '!==' against an empty array literal always produces the same result
• E0345: using equality or inequality operators against an object literal always produces the same result
• E0346: using '==' against a regular expression literal always returns 'false'
• E0347: duplicated case clause in switch statement
• E0348: unexpected '?' in type; use '| void' to make an optional type
• E0349: function parameter cannot be parenthesized
• E0358: 'declare' should not be written inside a 'declare namespace'
• E0369: nullish coalescing operator does nothing when left operand is never null
• E0373: unexpected whitespace between '!' and '=='; '!' here treated as the TypeScript non-null assertion operator
• E0374: unexpected whitespace between '!' and '=='
• E0376: JSX prop is missing an expression
• E0379: optional parameter cannot be followed by a required parameter
• E0381: Typescript does not allow keywords to contain escape sequence
• E0383: variable assignment to self is no-op
• E0427: missing 'break;' or '// fallthrough' comment between statement and 'case'
• E0450: misleading use of ',' operator in index
• E0451: misleading use of ',' operator in conditional statement
• E0452: empty parenthesis after control statement
• E0458: typeof result is of type string and so will never equal undefined; use 'undefined' instead
• E0707: classes cannot be named 'await' in async function
• E0708: unexpected '...'; expected expression
• E0709: expected variable name after '...'
• E0710: '^' is the XOR operator; to exponentiate, use '**' instead
• E0711: missing expression in placeholder within template literal
• E0712: missing ',' between array elements
• E0713: getters and setters cannot be generators
• E0714: 'async' keyword is not allowed on getters or setters
• E0715: cannot use multiple export default statements in one module
• E0716: unintuitive operator precedence when using & and << or >>
• E0717: namespace alias cannot use 'import type'
• E0718: using a '.' after a '?.' might fail, since '?.' might return 'undefined'
• E0719: TypeScript namespace aliases are not allowed in JavaScript
• E0720: function 'let' call may be confused for destructuring; remove parentheses to declare a variable