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parseInt() - JavaScript | MDN
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parseInt()

Baseline

20157

parseInt() 

console.log(parseInt("123"));
// 123 (default base-10)
console.log(parseInt("123", 10));
// 123 (explicitly specify base-10)
console.log(parseInt("   123 "));
// 123 (whitespace is ignored)
console.log(parseInt("077"));
// 77 (leading zeros are ignored)
console.log(parseInt("1.9"));
// 1 (decimal part is truncated)
console.log(parseInt("ff", 16));
// 255 (lower-case hexadecimal)
console.log(parseInt("0xFF", 16));
// 255 (upper-case hexadecimal with "0x" prefix)
console.log(parseInt("xyz"));
// NaN (input can't be converted to an integer)

js
parseInt(string)
parseInt(string, radix)

string

radix

2 36 string 32 0 [2, 36] NaN 0 string 10 radix

string NaN

  • radix 32 2 36

: JavaScript parseInt() parseFloat() parseInt("42") parseFloat("42") 42

parseInt 1 NaN

NaN 1 radix (radix 10 10 8 8 16 16 )

radix 0NaNInfinity undefined NaN JavaScript

  1. string +/- 0x 0X X radix 16 16
  2. string 10 10

: 0b parseInt() parseInt() 0 8 parseInt() 16 0x 0X radix 10 Number() BigInt()

16 parseInt() (+/-) 0x 0X

[2, 36] parseInt NaN

10 9 16 16 A F

parseInt 2 + -

parseInt radix parseInt("2", 2) 2 2 NaN 1e3 parseFloat() 1000 parseInt("1e3", 10) 1 e 10 .

parseInt NaN

NaN Number.isNaN parseInt NaN NaN NaN

e 6.022E23 6.022 10^23 parseInt parseInt Math.trunc()

thatNumber.toString(radix)

parseInt() BigInt() BigInt

parseInt()

15

js
parseInt("0xF", 16);
parseInt("F", 16);
parseInt("17", 8);
parseInt("015", 10);
parseInt("15,123", 10);
parseInt("FXX123", 16);
parseInt("1111", 2);
parseInt("15 * 3", 10);
parseInt("15e2", 10);
parseInt("15px", 10);
parseInt("12", 13);

NaN

js
parseInt("Hello", 8); // 
parseInt("546", 2); // 2  0  1

-15

js
parseInt("-F", 16);
parseInt("-0F", 16);
parseInt("-0XF", 16);
parseInt("-17", 8);
parseInt("-15", 10);
parseInt("-1111", 2);
parseInt("-15e1", 10);
parseInt("-12", 13);

224

js
parseInt("0e0", 16);

parseInt() BigInt n

js
parseInt("900719925474099267n");
// 900719925474099300

n BigInt()

js
BigInt("900719925474099267");
// 900719925474099267n

parseInt

js
parseInt("123_456"); // 123

parseInt()

parseInt() 36

js
parseInt(null, 36); // 1112745: "null"  36  1112745
parseInt(undefined, 36); // 86464843759093: "undefined"  36  86464843759093

parseInt() Math.trunc()

js
parseInt(15.99, 10); // 15
parseInt(-15.1, 10); // -15

("15.99", "-15.1") parseInt() 1e+21 1e-7 ("1.5e+22", "1.51e-8") parseInt() e parseInt() 1

js
parseInt(4.7 * 1e22, 10); //  4 
parseInt(0.00000000000434, 10); //  4 

parseInt(0.0000001, 10); // 1
parseInt(0.000000123, 10); // 1
parseInt(1e-7, 10); // 1
parseInt(1000000000000000000000, 10); // 1
parseInt(123000000000000000000000, 10); // 1
parseInt(1e21, 10); // 1

ECMAScript 2027 LanguageSpecification
# sec-parseint-string-radix

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    1. AggregateError: No Promise in Promise.any was resolved
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    21. SyntaxError: "0"-prefixed octal literals and octal escape seq. are deprecated
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    33. SyntaxError: duplicate capture group name in regular expression
    34. SyntaxError: duplicate formal argument x
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    39. SyntaxError: getter functions must have no arguments
    40. SyntaxError: identifier starts immediately after numeric literal
    41. SyntaxError: illegal character
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    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
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    58. SyntaxError: label not found
    59. SyntaxError: missing : after property id
    60. SyntaxError: missing ) after argument list
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    63. SyntaxError: missing } after function body
    64. SyntaxError: missing } after property list
    65. SyntaxError: missing = in const declaration
    66. SyntaxError: missing formal parameter
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    71. SyntaxError: nothing to repeat
    72. SyntaxError: numbers out of order in {} quantifier.
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    74. SyntaxError: parameter after rest parameter
    75. SyntaxError: private fields can't be deleted
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    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: cannot use 'in' operator to search for 'x' in 'y'
    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"
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    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. TypeError: 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
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