A little refactoring.

Author: kshetline

lib/parse.js

@@ -411,9 +411,8 @@ function parse(text, reviver, newOptions) {
     // Shouldn't be able to reach here with tokens other than type 'eof'.
   }
 
-  function parseNumber() {
-    read();
-    literal('aN');
+  function parseSymbolicNumber(text, value) {
+    literal(text);
 
     if (peek() === UNDERSCORE) {
       read();
@@ -422,19 +421,19 @@ function parse(text, reviver, newOptions) {
 
     if (peek() === LOWER_m) {
       read();
-      return newPrimitiveToken(big.getBigDecimalType(), big.toBigDecimal(NaN));
+      return newPrimitiveToken(big.getBigDecimalType(), big.toBigDecimal(value));
     }
 
     if (peek() === LOWER_d) {
       read();
-      return newPrimitiveToken(getDecimalType(), big.toDecimal(NaN));
+      return newPrimitiveToken(getDecimalType(), big.toDecimal(value));
     }
 
     if (trailingUnderscore) {
       throw invalidChar('_');
     }
 
-    return newPrimitiveToken('number', NaN);
+    return newPrimitiveToken('number', value);
   }
 
   // Faster string reading based on https://github.com/json5/json5/pull/233, by @jlguardi
@@ -645,32 +644,10 @@ function parse(text, reviver, newOptions) {
         return;
 
       case UPPER_I:
-        read();
-        literal('nfinity');
-
-        if (peek() === UNDERSCORE) {
-          read();
-          trailingUnderscore = true;
-        }
-
-        if (peek() === LOWER_m) {
-          read();
-          return newPrimitiveToken(big.getBigDecimalType(), big.toBigDecimal(Infinity));
-        }
-
-        if (peek() === LOWER_d) {
-          read();
-          return newPrimitiveToken(getDecimalType(), big.toDecimal(Infinity));
-        }
-
-        if (trailingUnderscore) {
-          throw invalidChar('_');
-        }
-
-        return newPrimitiveToken('number', Infinity);
+        return parseSymbolicNumber('Infinity', Infinity);
 
       case UPPER_N:
-        return parseNumber();
+        return parseSymbolicNumber('NaN', NaN);
 
       case SINGLE_QUOTE:
       case QUOTE:
@@ -756,8 +733,6 @@ function parse(text, reviver, newOptions) {
   }
 
   function lexSign() {
-    let trailingUnderscore = false;
-
     switch (c) {
       case DOT:
         buffer = readChar();
@@ -788,32 +763,10 @@ function parse(text, reviver, newOptions) {
         return;
 
       case UPPER_I:
-        read();
-        literal('nfinity');
-
-        if (peek() === UNDERSCORE) {
-          read();
-          trailingUnderscore = true;
-        }
-
-        if (peek() === LOWER_m) {
-          read();
-          return newPrimitiveToken(big.getBigDecimalType(), big.toBigDecimal(sign * Infinity));
-        }
-
-        if (peek() === LOWER_d) {
-          read();
-          return newPrimitiveToken(getDecimalType(), big.toDecimal(sign * Infinity));
-        }
-
-        if (trailingUnderscore) {
-          throw invalidChar('_');
-        }
-
-        return newPrimitiveToken('number', sign * Infinity);
+        return parseSymbolicNumber('Infinity', sign * Infinity);
 
       case UPPER_N:
-        return parseNumber();
+        return parseSymbolicNumber('NaN', NaN);
     }
 
     throw invalidChar(read());