其余参数

其余参数 句法允许将不定数目的自变量表示成数组。

句法

function f(a, b, ...theArgs) {
  // ...
}
					

描述

函数的最后参数可以加前缀采用 ... which will cause all remaining (user supplied) arguments to be placed within a "standard" JavaScript array.

仅最后参数可以是其余参数。

function myFun(a, b, ...manyMoreArgs) {
  console.log("a", a)
  console.log("b", b)
  console.log("manyMoreArgs", manyMoreArgs)
}
myFun("one", "two", "three", "four", "five", "six")
// Console Output:
// a, one
// b, two
// manyMoreArgs, [three, four, five, six]
					

区别其余参数和 arguments object

有 3 个主要区别介于其余参数和 arguments 对象:

  • rest parameters are only the ones that haven't been given a separate name (i.e. formally defined in function expression), while the arguments object contains all arguments passed to the function;
  • the arguments object is not a real array, while rest parameters are Array instances, meaning methods like sort , map , forEach or pop can be applied on it directly;
  • the arguments object has additional functionality specific to itself (like the callee property).

从自变量到数组

Rest parameters have been introduced to reduce the boilerplate code that was induced by the arguments

// Before rest parameters, "arguments" could be converted to a normal array using:
function f(a, b) {
  let normalArray = Array.prototype.slice.call(arguments)
  // -- or --
  let normalArray = [].slice.call(arguments)
  // -- or --
  let normalArray = Array.from(arguments)
  let first = normalArray.shift()  // OK, gives the first argument
  let first = arguments.shift()    // ERROR (arguments is not a normal array)
}
// Now, you can easily gain access to a normal array using a rest parameter
function f(...args) {
  let normalArray = args
  let first = normalArray.shift() // OK, gives the first argument
}
					

范例

使用其余参数

In this example, the first argument is mapped to a and the second to b , so these named arguments are used as normal.

However, the third argument, manyMoreArgs , will be an array that contains the 3 rd , 4 th , 5 th , 6 th ... n th — as many arguments that the user includes.

function myFun(a, b, ...manyMoreArgs) {
  console.log("a", a)
  console.log("b", b)
  console.log("manyMoreArgs", manyMoreArgs)
}
myFun("one", "two", "three", "four", "five", "six")
// a, one
// b, two
// manyMoreArgs, [three, four, five, six]
					

Below... even though there is just one value, the last argument still gets put into an array.

// using the same function definition from example above
myFun("one", "two", "three")
// a, one
// b, two
// manyMoreArgs, [three]
					

Below, the third argument isn't provided, but manyMoreArgs is still an array (albeit an empty one).

// using the same function definition from example above
myFun("one", "two")
// a, one
// b, two
// manyMoreArgs, []
					

自变量长度

Since theArgs is an array, a count of its elements is given by the length 特性:

function fun1(...theArgs) {
  console.log(theArgs.length)
}
fun1()         // 0
fun1(5)        // 1
fun1(5, 6, 7)  // 3
					

普通参数和其余参数

In the next example, a rest parameter is used to collect all parameters after the first into an array. Each one of them is then multiplied by the first parameter, and the array is returned:

function multiply(multiplier, ...theArgs) {
  return theArgs.map(element => {
    return multiplier * element
  })
}
let arr = multiply(2, 1, 2, 3)
console.log(arr)  // [2, 4, 6]
					

与自变量对象一起使用

Array methods can be used on rest parameters, but not on the arguments 对象:

function sortRestArgs(...theArgs) {
  let sortedArgs = theArgs.sort()
  return sortedArgs
}
console.log(sortRestArgs(5, 3, 7, 1)) // 1, 3, 5, 7
function sortArguments() {
  let sortedArgs = arguments.sort()
  return sortedArgs  // this will never happen
}
console.log(sortArguments(5, 3, 7, 1))
// throws a TypeError (arguments.sort is not a function)
					

要使用 Array 方法在 arguments 对象,必须把它先转换为真正的数组。

function sortArguments() {
  let args = Array.from(arguments)
  let sortedArgs = args.sort()
  return sortedArgs
}
console.log(sortArguments(5, 3, 7, 1))  // 1, 3, 5, 7
					

规范

规范
ECMAScript (ECMA-262)
The definition of 'Function Definitions' in that specification.

浏览器兼容性

更新 GitHub 上的兼容性数据
Desktop Mobile Server
Chrome Edge Firefox Internet Explorer Opera Safari Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet Node.js
其余参数 Chrome 47 Edge 12 Firefox 15 IE No Opera 34 Safari 10 WebView Android 47 Chrome Android 47 Firefox Android 15 Opera Android 34 Safari iOS 10 Samsung Internet Android 5.0 nodejs 6.0.0
6.0.0
4.0.0
Disabled
Disabled From version 4.0.0: this feature is behind the --harmony runtime flag.
析构其余参数 Chrome 49 Edge 79 Firefox 52 IE No Opera 36 Safari 10 WebView Android 49 Chrome Android 49 Firefox Android 52 Opera Android 36 Safari iOS 10 Samsung Internet Android 5.0 nodejs Yes

图例

完整支持
完整支持
不支持
不支持
用户必须明确启用此特征。
用户必须明确启用此特征。

另请参阅

Metadata

  1. JavaScript
  2. 教程:
  3. 完整初学者
    1. JavaScript 基础
    2. JavaScript 第一步
    3. JavaScript 构建块
    4. 引入 JavaScript 对象
  4. JavaScript 指南
    1. 介绍
    2. 语法和类型
    3. 控制流程和错误处理
    4. 循环和迭代
    5. 函数
    6. 表达式和运算符
    7. 数字和日期
    8. 文本格式
    9. 正则表达式
    10. Indexed collections
    11. Keyed collections
    12. Working with objects
    13. 对象模型的细节
    14. Using promises
    15. 迭代器和生成器
    16. Meta programming
    17. JavaScript 模块
  5. 中间体
    1. Client-side JavaScript frameworks
    2. 客户端侧 Web API
    3. 重新介绍 JavaScript
    4. JavaScript 数据结构
    5. 相等比较和相同
    6. 闭包
  6. 高级
    1. 继承和原型链
    2. 严格模式
    3. JavaScript 类型数组
    4. 内存管理
    5. 并发模型和事件循环
  7. 参考:
  8. 内置对象
    1. AggregateError
    2. Array
    3. ArrayBuffer
    4. AsyncFunction
    5. Atomics
    6. BigInt
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    50. WeakMap
    51. WeakRef
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    53. WebAssembly
    54. decodeURI()
    55. decodeURIComponent()
    56. encodeURI()
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    59. eval()
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    61. isFinite()
    62. isNaN()
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    65. parseInt()
    66. undefined
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  9. 表达式 & 运算符
    1. Addition (+)
    2. Addition assignment (+=)
    3. Assignment (=)
    4. Bitwise AND (&)
    5. Bitwise AND assignment (&=)
    6. Bitwise NOT (~)
    7. Bitwise OR (|)
    8. Bitwise OR assignment (|=)
    9. Bitwise XOR (^)
    10. Bitwise XOR assignment (^=)
    11. Comma operator (,)
    12. 条件 (三元) 运算符
    13. Decrement (--)
    14. Destructuring assignment
    15. Division (/)
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    17. Equality (==)
    18. Exponentiation (**)
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    20. Function expression
    21. Greater than (>)
    22. Greater than or equal (>=)
    23. Grouping operator ( )
    24. Increment (++)
    25. Inequality (!=)
    26. Left shift (<<)
    27. Left shift assignment (<<=)
    28. Less than (<)
    29. Less than or equal (<=)
    30. Logical AND (&&)
    31. Logical AND assignment (&&=)
    32. Logical NOT (!)
    33. Logical OR (||)
    34. Logical OR assignment (||=)
    35. Logical nullish assignment (??=)
    36. Multiplication (*)
    37. Multiplication assignment (*=)
    38. Nullish coalescing operator (??)
    39. Object initializer
    40. 运算符优先级
    41. Optional chaining (?.)
    42. Pipeline operator (|>)
    43. 特性访问器
    44. Remainder (%)
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    46. Right shift (>>)
    47. Right shift assignment (>>=)
    48. Spread syntax (...)
    49. Strict equality (===)
    50. Strict inequality (!==)
    51. Subtraction (-)
    52. Subtraction assignment (-=)
    53. Unary negation (-)
    54. Unary plus (+)
    55. Unsigned right shift (>>>)
    56. Unsigned right shift assignment (>>>=)
    57. 异步函数表达式
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  11. 函数
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    2. 默认参数
    3. 方法定义
    4. 其余参数
    5. 自变量对象
    6. getter
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    3. 构造函数
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  12. 错误
    1. Error: Permission denied to access property "x"
    2. InternalError: too much recursion
    3. RangeError: argument is not a valid code point
    4. RangeError: invalid array length
    5. RangeError: invalid date
    6. RangeError: precision is out of range
    7. RangeError: radix must be an integer
    8. RangeError: repeat count must be less than infinity
    9. RangeError: repeat count must be non-negative
    10. ReferenceError: "x" is not defined
    11. ReferenceError: assignment to undeclared variable "x"
    12. ReferenceError: can't access lexical declaration`X' before initialization
    13. ReferenceError: deprecated caller or arguments usage
    14. ReferenceError: invalid assignment left-hand side
    15. ReferenceError: reference to undefined property "x"
    16. SyntaxError: "0"-prefixed octal literals and octal escape seq. are deprecated
    17. SyntaxError: "use strict" not allowed in function with non-simple parameters
    18. SyntaxError: "x" is a reserved identifier
    19. SyntaxError: JSON.parse: bad parsing
    20. SyntaxError: Malformed formal parameter
    21. SyntaxError: Unexpected token
    22. SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead
    23. SyntaxError: a declaration in the head of a for-of loop can't have an initializer
    24. SyntaxError: applying the 'delete' operator to an unqualified name is deprecated
    25. SyntaxError: for-in loop head declarations may not have initializers
    26. SyntaxError: function statement requires a name
    27. SyntaxError: identifier starts immediately after numeric literal
    28. SyntaxError: illegal character
    29. SyntaxError: invalid regular expression flag "x"
    30. SyntaxError: missing ) after argument list
    31. SyntaxError: missing ) after condition
    32. SyntaxError: missing : after property id
    33. SyntaxError: missing ; before statement
    34. SyntaxError: missing = in const declaration
    35. SyntaxError: missing ] after element list
    36. SyntaxError: missing formal parameter
    37. SyntaxError: missing name after . operator
    38. SyntaxError: missing variable name
    39. SyntaxError: missing } after function body
    40. SyntaxError: missing } after property list
    41. SyntaxError: redeclaration of formal parameter "x"
    42. SyntaxError: return not in function
    43. SyntaxError: test for equality (==) mistyped as assignment (=)?
    44. SyntaxError: unterminated string literal
    45. TypeError: "x" has no properties
    46. TypeError: "x" is (not) "y"
    47. TypeError: "x" is not a constructor
    48. TypeError: "x" is not a function
    49. TypeError: "x" is not a non-null object
    50. TypeError: "x" is read-only
    51. TypeError: 'x' is not iterable
    52. TypeError: More arguments needed
    53. TypeError: Reduce of empty array with no initial value
    54. TypeError: X.prototype.y called on incompatible type
    55. TypeError: can't access dead object
    56. TypeError: can't access property "x" of "y"
    57. TypeError: can't assign to property "x" on "y": not an object
    58. TypeError: can't define property "x": "obj" is not extensible
    59. TypeError: can't delete non-configurable array element
    60. TypeError: can't redefine non-configurable property "x"
    61. TypeError: cannot use 'in' operator to search for 'x' in 'y'
    62. TypeError: cyclic object value
    63. TypeError: invalid 'instanceof' operand 'x'
    64. TypeError: invalid Array.prototype.sort argument
    65. TypeError: invalid arguments
    66. TypeError: invalid assignment to const "x"
    67. TypeError: property "x" is non-configurable and can't be deleted
    68. TypeError: setting getter-only property "x"
    69. TypeError: variable "x" redeclares argument
    70. URIError: malformed URI sequence
    71. Warning: -file- is being assigned a //# sourceMappingURL, but already has one
    72. Warning: 08/09 is not a legal ECMA-262 octal constant
    73. Warning: Date.prototype.toLocaleFormat is deprecated
    74. Warning: JavaScript 1.6's for-each-in loops are deprecated
    75. Warning: String.x is deprecated; use String.prototype.x instead
    76. Warning: expression closures are deprecated
    77. Warning: unreachable code after return statement
  13. 杂项
    1. JavaScript technologies overview
    2. 词汇语法
    3. JavaScript 数据结构
    4. Enumerability and ownership of properties
    5. Iteration protocols
    6. 严格模式
    7. Transitioning to strict mode
    8. Template literals
    9. 弃用特征