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title: '`{BigInt,Number}.fromString`'
status: proposal
stage: 1
location: https://mathiasbynens.github.io/proposal-number-fromstring/
copyright: false
contributors: Mathias Bynens
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<emu-clause id="sec-bigint-fromstring-string-radix">
  <h1>BigInt.fromString ( _string_, _radix_ )</h1>
  <p>The `BigInt.fromString` function produces an integer value dictated by interpretation of the contents of the _string_ argument according to the specified _radix_. If _radix_ is *undefined*, it is assumed to be 10.</p>
  <p>When the `BigInt.fromString` function is called, the following steps are taken:</p>
  <emu-alg>
    1. If Type(_string_) is not String, throw a *TypeError* exception.
    1. If _string_ is empty, throw a *SyntaxError* exception.
    1. Let _sign_ be 1.
    1. If the first code unit of _string_ is the code unit 0x002D (HYPHEN-MINUS), then
      1. Let _sign_ be -1.
      1. Remove the first code unit from _string_.
      1. If _string_ is empty, throw a *SyntaxError* exception.
    1. If _radix_ is not present, let _R_ be 10.
    1. Else if _radix_ is *undefined*, let _R_ be 10.
    1. Else, let _R_ be ? ToInteger(_radix_).
    1. If _R_ &lt; 2 or _R_ &gt; 36, throw a *RangeError* exception.
    1. If _string_ represents a mathematical integer value in radix-_R_ notation, using the characters <b>0</b>-<b>9</b> for digits with values 0 to 9, and the letters <b>a</b>-<b>z</b> for digits with values 10 through 35, then
      1. Let _mathInt_ be that mathematical integer value.
    1. Else, throw a *SyntaxError* exception.
    1. Let _number_ be _sign_ &times; _mathInt_.
    1. Return the BigInt value for _number_.
  </emu-alg>
</emu-clause>
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<emu-clause id="sec-number-fromstring-string-radix">
  <h1>Number.fromString ( _string_, _radix_ )</h1>
  <p>The `Number.fromString` function produces a numeric value dictated by interpretation of the contents of the _string_ argument according to the specified _radix_. If _radix_ is *undefined*, it is assumed to be 10.</p>
  <p>When the `Number.fromString` function is called, the following steps are taken:</p>
  <emu-alg>
    1. If Type(_string_) is not String, throw a *TypeError* exception.
    1. If _string_ is empty, throw a *SyntaxError* exception.
    1. Let _sign_ be 1.
    1. If the first code unit of _string_ is the code unit 0x002D (HYPHEN-MINUS), then
      1. Let _sign_ be -1.
      1. Remove the first code unit from _string_.
      1. If _string_ is empty, throw a *SyntaxError* exception.
    1. If _radix_ is not present, let _R_ be 10.
    1. Else if _radix_ is *undefined*, let _R_ be 10.
    1. Else, let _R_ be ? ToInteger(_radix_).
    1. If _R_ &lt; 2 or _R_ &gt; 36, throw a *RangeError* exception.
    1. If _string_ represents a mathematical number value in radix-_R_ notation, using the characters <b>0</b>-<b>9</b> for digits with values 0 to 9, and the letters <b>a</b>-<b>z</b> for digits with values 10 through 35, then
      1. Let _mathNum_ be that mathematical number value.
    1. Else, throw a *SyntaxError* exception.
    1. Let _number_ be _sign_ &times; _mathNum_.
    1. Return the Number value for _number_.
  </emu-alg>
</emu-clause>