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TypeError: "x" is read-only

报错消息

TypeError: "x" is read-only (Firefox) //格式错误："x"只读。(x 可以代表任意值) TypeError: 0 is read-only (Firefox) TypeError: Cannot assign to read only property 'x' of #<Object> (Chrome) //格式错误：对象的 x 属性是只读的不能设置（chrome） TypeError: Cannot assign to read only property '0' of [object Array] (Chrome)

本文内容

错误格式

TypeError

哪里出错了？

全局变量或对象属性被设置为只读 (专业点讲，就是这条数据属性禁止写入.)

这条错误值发生在strict mode code(俗称严格模式). 正常情况下，是没有报错的。

例如

无效例子（也就是下面这么做会导致报这种错）

只读属性不能直接创建，但我们可以通过Object.defineProperty() 或 Object.freeze()设置。

js
"use strict"; var obj = Object.freeze({name: "Elsa", score: 157}); obj.score = 0; // TypeError "use strict"; Object.defineProperty(this, "LUNG_COUNT", {value: 2, writable: false}); LUNG_COUNT = 3; // TypeError "use strict"; var frozenArray = Object.freeze([0, 1, 2]); frozenArray[0]++; // TypeError 还有几个 JavaScript 内置属性。如果你尝试修改一个常量。 "use strict"; Math.PI = 4; // TypeError

傻了吧，报错了

全局变量 undefined 也是只读的, 所以你不能忽视臭名昭著的"undefined is not a function"错误：

js
"use strict"; undefined = function () {}; // TypeError: "undefined" is read-only

下面这样都是有效，不报错的

js
"use strict"; var obj = Object.freeze({ name: "Score", points: 157 }); obj = { name: obj.name, points: 0 }; // 用一个新对象替换原来的对象 (其实就是更改了对象的指针) ("use strict"); var LUNG_COUNT = 2; // LUNG_COUNT = 3; //

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  1. JavaScript
  2. 教程
  3. JavaScript 指南
    1. 介绍
    2. 语法和数据类型
    3. 流程控制与错误处理
    4. 循环与迭代
    5. 函数
    6. 表达式与运算符
    7. 数字与字符串
    8. 表达日期与时间
    9. 正则表达式
    10. 索引集合类
    11. 带键的集合
    12. 使用对象
    13. 使用类
    14. 使用 Promise
    15. JavaScript 类型化数组
    16. 迭代器和生成器
    17. 资源管理
    18. 国际化
    19. JavaScript 模块
  4. 中级
    1. 语言概述
    2. JavaScript 数据结构
    3. 如何正确判断相等性
    4. 属性的可枚举性和所有权
    5. 闭包
  5. 高级
    1. 继承和原型链
    2. 元编程
    3. 内存管理
  6. 参考
  7. 内置对象
    1. AggregateError
    2. Array
    3. ArrayBuffer
    4. AsyncDisposableStack
    5. AsyncFunction
    6. AsyncGenerator
    7. AsyncGeneratorFunction
    8. AsyncIterator
    9. Atomics
    10. BigInt
    11. BigInt64Array
    12. BigUint64Array
    13. Boolean
    14. DataView
    15. Date
    16. decodeURI()
    17. decodeURIComponent()
    18. DisposableStack
    19. encodeURI()
    20. encodeURIComponent()
    21. Error
    22. escape()
    23. eval()
    24. EvalError
    25. FinalizationRegistry
    26. Float16Array
    27. Float32Array
    28. Float64Array
    29. Function
    30. Generator
    31. GeneratorFunction
    32. globalThis
    33. Infinity
    34. Int8Array
    35. Int16Array
    36. Int32Array
    37. InternalError
    38. Intl
    39. isFinite()
    40. isNaN()
    41. Iterator
    42. JSON
    43. Map
    44. Math
    45. NaN
    46. Number
    47. Object
    48. parseFloat
    49. parseInt
    50. Promise
    51. Proxy
    52. RangeError
    53. ReferenceError
    54. Reflect
    55. RegExp
    56. Set
    57. SharedArrayBuffer
    58. String
    59. SuppressedError
    60. Symbol
    61. SyntaxError
    62. Temporal
    63. TypedArray
    64. TypeError
    65. Uint8Array
    66. Uint8ClampedArray
    67. Uint16Array
    68. Uint32Array
    69. undefined
    70. unescape()
    71. URIError
    72. WeakMap
    73. WeakRef
    74. WeakSet
  8. 表达式和运算符
    1. 加法（+）
    2. 加法赋值（+=）
    3. 赋值（=）
    4. 异步函数（async function）表达式
    5. async function* 表达式
    6. await
    7. 按位与（&）
    8. 按位与赋值（&=）
    9. 按位非（~）
    10. 按位或（|）
    11. 按位或赋值（|=）
    12. 按位异或（^）
    13. 按位异或赋值 (^=)
    14. 类表达式
    15. 逗号运算符（,）
    16. 条件（三元）运算符
    17. 自减（--）
    18. delete 运算符
    19. 解构
    20. 除法（/）
    21. 除法赋值（/=）
    22. 相等（==）
    23. 幂（**）
    24. 幂赋值（**=）
    25. 函数表达式
    26. function* 表达式
    27. 大于（>）
    28. 大于等于（>=）
    29. 圆括号运算符
    30. import.meta
      1. import.meta.resolve()
    31. import()
    32. in
    33. 自增（++）
    34. 不相等（!=）
    35. instanceof
    36. 左移 (<<)
    37. 左移赋值（<<=）
    38. 小于（<）
    39. 小于等于（<=）
    40. 逻辑与（&&）
    41. 逻辑与赋值（&&=）
    42. 逻辑非（!）
    43. 逻辑或（||）
    44. 逻辑或赋值（||=）
    45. 乘法（*）
    46. 乘法赋值（*=）
    47. new
    48. new.target
    49. null
    50. 逻辑空赋值（??=）
    51. 空值合并运算符（??）
    52. 对象初始化器
    53. 运算符优先级
    54. 可选链运算符（?.）
    55. 属性访问器
    56. 取余（%）
    57. 取余赋值（%=）
    58. 右移（>>）
    59. 右移赋值（>>=）
    60. 展开语法（...）
    61. 严格相等（===）
    62. 严格不相等（!==）
    63. 减法（-）
    64. 减法赋值（-=）
    65. super
    66. this
    67. typeof
    68. 一元减（-）
    69. 一元加（+）
    70. 无符号右移（>>>）
    71. 无符号右移赋值（>>>=）
    72. void 运算符
    73. yield
    74. yield*
  9. 语句和声明
    1. async function
    2. async function*
    3. await using
    4. 块语句
    5. break
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    2. 默认参数值
    3. getter
    4. 方法的定义
    5. 剩余参数
    6. setter
    7. arguments 对象
      1. arguments[Symbol.iterator]()
      2. arguments.callee
      3. arguments.length
  11. 类
    1. 构造函数
    2. extends
    3. 私有元素
    4. 公有类字段
    5. static
    6. 静态初始化块
  12. 正则表达式
    1. 反向引用：\1、\2
    2. Capturing group: (...)
    3. Character class escape: \d, \D, \w, \W, \s, \S
    4. Character class: [...], [^...]
    5. 字符转义：\n、\u{...}
    6. Disjunction: |
    7. 输入边界断言：^、$
    8. 字面字符：a、b
    9. Lookahead assertion: (?=...), (?!...)
    10. Lookbehind assertion: (?<=...), (?<!...)
    11. Modifier: (?ims-ims:...)
    12. Named backreference: \k<name>
    13. Named capturing group: (?<name>...)
    14. Non-capturing group: (?:...)
    15. 量词：*、+、?、{n}、{n,}、{n,m}
    16. Unicode 字符类转义：\p{...}、\P{...}
    17. 通配符：.
    18. 单词边界断言：\b、\B
  13. 错误
    1. AggregateError: No Promise in Promise.any was resolved
    2. Error: Permission denied to access property "x"
    3. InternalError: too much recursion
    4. RangeError: argument is not a valid code point
    5. RangeError: BigInt division by zero
    6. RangeError: BigInt negative exponent
    7. RangeError: form must be one of 'NFC', 'NFD', 'NFKC', or 'NFKD'
    8. RangeError: invalid array length
    9. RangeError: invalid date
    10. RangeError: precision is out of range
    11. RangeError: radix must be an integer
    12. RangeError: repeat count must be less than infinity
    13. RangeError: repeat count must be non-negative
    14. RangeError: x can't be converted to BigInt because it isn't an integer
    15. ReferenceError: "x" is not defined
    16. ReferenceError: assignment to undeclared variable "x"
    17. ReferenceError: can't access lexical declaration`X' before initialization
    18. ReferenceError: must call super constructor before using 'this' in derived class constructor
    19. ReferenceError: super() called twice in derived class constructor
    20. SyntaxError: 'arguments'/'eval' can't be defined or assigned to in strict mode code
    21. SyntaxError: "0"-prefixed octal literals are deprecated
    22. SyntaxError: "use strict" not allowed in function with non-simple parameters
    23. SyntaxError: "x" is a reserved identifier
    24. SyntaxError: \ at end of pattern
    25. SyntaxError: a declaration in the head of a for-of loop can't have an initializer
    26. SyntaxError: applying the 'delete' operator to an unqualified name is deprecated
    27. SyntaxError: arguments is not valid in fields
    28. SyntaxError: await is only valid in async functions, async generators and modules
    29. SyntaxError: await/yield expression can't be used in parameter
    30. SyntaxError: cannot use ?? unparenthesized within || and && expressions
    31. SyntaxError: character class escape cannot be used in class range in regular expression
    32. SyntaxError: continue must be inside loop
    33. SyntaxError: duplicate capture group name in regular expression
    34. SyntaxError: duplicate formal argument x
    35. SyntaxError: for-in loop head declarations may not have initializers
    36. SyntaxError: function statement requires a name
    37. SyntaxError: functions cannot be labelled
    38. SyntaxError: getter and setter for private name #x should either be both static or non-static
    39. SyntaxError: getter functions must have no arguments
    40. SyntaxError: identifier starts immediately after numeric literal
    41. SyntaxError: illegal character
    42. SyntaxError: import declarations may only appear at top level of a module
    43. SyntaxError: incomplete quantifier in regular expression
    44. SyntaxError: invalid assignment left-hand side
    45. SyntaxError: invalid BigInt syntax
    46. SyntaxError: invalid capture group name in regular expression
    47. SyntaxError: invalid character in class in regular expression
    48. SyntaxError: invalid class set operation in regular expression
    49. SyntaxError: invalid decimal escape in regular expression
    50. SyntaxError: invalid identity escape in regular expression
    51. SyntaxError: invalid named capture reference in regular expression
    52. SyntaxError: invalid property name in regular expression
    53. SyntaxError: invalid range in character class
    54. SyntaxError: invalid regexp group
    55. SyntaxError: invalid regular expression flag "x"
    56. SyntaxError: invalid unicode escape in regular expression
    57. SyntaxError: JSON.parse: bad parsing
    58. SyntaxError: label not found
    59. SyntaxError: missing : after property id
    60. SyntaxError: missing ) after argument list
    61. SyntaxError: missing ) after condition
    62. SyntaxError: missing ] after element list
    63. SyntaxError: missing } after function body
    64. SyntaxError: missing } after property list
    65. SyntaxError: missing = in const declaration
    66. SyntaxError: missing formal parameter
    67. SyntaxError: missing name after . operator
    68. SyntaxError: missing variable name
    69. SyntaxError: negated character class with strings in regular expression
    70. SyntaxError: new keyword cannot be used with an optional chain
    71. SyntaxError: nothing to repeat
    72. SyntaxError: numbers out of order in {} quantifier.
    73. SyntaxError: octal escape sequences can't be used in untagged template literals or in strict mode code
    74. SyntaxError: parameter after rest parameter
    75. SyntaxError: private fields can't be deleted
    76. SyntaxError: property name __proto__ appears more than once in object literal
    77. SyntaxError: raw bracket is not allowed in regular expression with unicode flag
    78. SyntaxError: redeclaration of formal parameter "x"
    79. SyntaxError: reference to undeclared private field or method #x
    80. SyntaxError: rest parameter may not have a default
    81. SyntaxError: return not in function
    82. SyntaxError: setter functions must have one argument
    83. SyntaxError: string literal contains an unescaped line break
    84. SyntaxError: super() is only valid in derived class constructors
    85. SyntaxError: tagged template cannot be used with optional chain
    86. SyntaxError: Unexpected '#' used outside of class body
    87. SyntaxError: Unexpected token
    88. SyntaxError: unlabeled break must be inside loop or switch
    89. SyntaxError: unparenthesized unary expression can't appear on the left-hand side of '**'
    90. SyntaxError: use of super property/member accesses only valid within methods or eval code within methods
    91. SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead
    92. ReferenceError: deprecated caller or arguments usage
    93. TypeError: 'x' is not iterable
    94. TypeError: "x" is (not) "y"
    95. TypeError: "x" is not a constructor
    96. TypeError: "x" is not a function
    97. TypeError: "x" is not a non-null object
    98. TypeError: "x" is read-only
    99. TypeError: already executing generator
    100. TypeError: BigInt value can't be serialized in JSON
    101. TypeError: calling a builtin X constructor without new is forbidden
    102. TypeError: can't access/set private field or method: object is not the right class
    103. TypeError: can't assign to property "x" on "y": not an object
    104. TypeError: can't convert BigInt to number
    105. TypeError: can't convert x to BigInt
    106. TypeError: can't define property "x": "obj" is not extensible
    107. TypeError: can't delete non-configurable array element
    108. TypeError: can't redefine non-configurable property "x"
    109. TypeError: can't set prototype of this object
    110. TypeError: can't set prototype: it would cause a prototype chain cycle
    111. TypeError: invalid 'in' operand "x"
    112. TypeError: class constructors must be invoked with 'new'
    113. TypeError: cyclic object value
    114. TypeError: derived class constructor returned invalid value x
    115. TypeError: getting private setter-only property
    116. TypeError: Initializing an object twice is an error with private fields/methods
    117. TypeError: invalid 'instanceof' operand 'x'
    118. TypeError: invalid Array.prototype.sort argument
    119. TypeError: invalid assignment to const "x"
    120. TypeError: Iterator/AsyncIterator constructor can't be used directly
    121. TypeError: matchAll/replaceAll must be called with a global RegExp
    122. TypeError: More arguments needed
    123. TypeError: "x" has no properties
    124. TypeError: property "x" is non-configurable and can't be deleted
    125. TypeError: Reduce of empty array with no initial value
    126. TypeError: setting getter-only property "x"
    127. TypeError: WeakSet key/WeakMap value 'x' must be an object or an unregistered symbol
    128. X.prototype.y called on incompatible type
    129. URIError: malformed URI sequence
    130. Warning: -file- is being assigned a //# sourceMappingURL, but already has one
    131. Warning: unreachable code after return statement
  14. 更多
    1. JavaScript 技术概要
    2. 运行模型
    3. 词法文法
    4. 迭代协议
    5. 严格模式
    6. 模板字符串
    7. 尾后逗号
    8. 已废弃的特性

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