Fix construction from [Symbol.toPrimitive] (#102)

Fixes #101.

Author: jakobkummerow

lib/jsbi.ts

@@ -1819,9 +1819,8 @@ class JSBI extends Array {
     if (obj.constructor === JSBI) return obj;
     if (typeof Symbol !== 'undefined' &&
           typeof Symbol.toPrimitive === 'symbol') {
-      const exoticToPrim = obj[Symbol.toPrimitive];
-      if (exoticToPrim) {
-        const primitive = exoticToPrim(hint);
+      if (obj[Symbol.toPrimitive]) {
+        const primitive = obj[Symbol.toPrimitive](hint);
         if (typeof primitive !== 'object') return primitive;
         throw new TypeError('Cannot convert object to primitive value');
       }

tests/tests.mjs

@@ -131,6 +131,16 @@ const TESTS = [
   }
 })();
 
+// https://github.com/GoogleChromeLabs/jsbi/issues/101
+(function() {
+  const o = {
+    num: 123,
+    [Symbol.toPrimitive]: function() { return this.num; }
+  };
+  const result = JSBI.BigInt(o);
+  assertTrue(JSBI.equal(result, JSBI.BigInt(123)));
+})();
+
 function parse(string) {
   if (string.charCodeAt(0) === 0x2D) { // '-'
     return JSBI.unaryMinus(JSBI.BigInt(string.slice(1)));