<emu-clause id="sec-bigint-parseint-string-radix">

<h1>BigInt.parseInt ( _string_, _radix_ )</h1>

<p>The `BigInt.parseInt` function produces an integer value dictated by interpretation of the contents of the _string_ argument according to the specified _radix_. Leading white space in _string_ is ignored. If _radix_ is *undefined* or 0, it is assumed to be 10 except when the number begins with the code unit pairs `0x` or `0X`, in which case a radix of 16 is assumed. If _radix_ is 16, the number may also optionally begin with the code unit pairs `0x` or `0X`.</p>

<p>When the `BigInt.parseInt` function is called, the following steps are taken:</p>

<emu-alg>

1. Let _inputString_ be ? ToString(_string_).

1. Let _S_ be a newly created substring of _inputString_ consisting of the first code unit that is not a |StrWhiteSpaceChar| and all code units following that code unit. (In other words, remove leading white space.) If _inputString_ does not contain any such code unit, let _S_ be the empty string.

1. Let _sign_ be 1.

1. If _S_ is not empty and the first code unit of _S_ is the code unit 0x002D (HYPHEN-MINUS), let _sign_ be -1.

1. If _S_ is not empty and the first code unit of _S_ is the code unit 0x002B (PLUS SIGN) or the code unit 0x002D (HYPHEN-MINUS), remove the first code unit from _S_.

1. Let _R_ be ? ToInt32(_radix_).

1. Let _stripPrefix_ be *true*.

1. If _R_ &ne; 0, then

1. If _R_ &lt; 2 or _R_ &gt; 36, throw a *SyntaxError* exception.

1. If _R_ &ne; 16, let _stripPrefix_ be *false*.

1. Else _R_ = 0,

1. Let _R_ be 10.

1. If _stripPrefix_ is *true*, then

1. If the length of _S_ is at least 2 and the first two code units of _S_ are either `"0x"` or `"0X"`, remove the first two code units from _S_ and let _R_ be 16.

1. If _S_ contains a code unit that is not a radix-_R_ digit, let _Z_ be the substring of _S_ consisting of all code units before the first such code unit; otherwise, let _Z_ be _S_.

1. If _Z_ is empty, throw a *SyntaxError* exception.

1. Let _mathInt_ be the mathematical integer value that is represented by _Z_ in radix-_R_ notation, using the letters <b>A</b>-<b>Z</b> and <b>a</b>-<b>z</b> for digits with values 10 through 35.

1. Let _number_ be _sign_ &times; _mathInt_.

1. Return the BigInt value for _number_.

</emu-alg>

<emu-note>

<p>`parseInt` may interpret only a leading portion of _string_ as an integer value; it ignores any code units that cannot be interpreted as part of the notation of an integer, and no indication is given that any such code units were ignored.</p>

</emu-note>

</emu-clause>