JSON中n是否为合法起始字符？解析"no"报错位置疑问

1. Is "n" a valid starting character for JSON? #

Absolutely! The only valid JSON value that starts with "n" is null—and since null is a fully valid top-level JSON value (or can be nested inside objects or arrays), "n" is indeed a valid starting character.

2. Why does parsing "not json" or "no" throw errors pointing to position 1 instead of the starting "n"? #

This all comes down to how JSON parsers (like the built-in one in Node.js) process input token by token. Here's the step-by-step breakdown:

• When the parser sees the first character "n", it immediately starts trying to match the null token—since that's the only valid JSON value starting with "n". To form null, it expects the next characters to be u, then l, then l.
• For input "no": After reading the "n" at position 0, it looks at position 1 and finds "o"—which isn't the "u" it needs to keep building the null token. At this point, the parser can't resolve the token it started constructing, so it throws an error pointing to the exact position where the mismatch happened (position 1), not the initial "n" that kicked off the attempt.
• For "not json": Same exact logic. The parser sees "n" at 0, expects "u" next, gets "o" at 1, and reports that as the error spot.
  It’s not that the parser doesn’t recognize "n" as a valid start—it’s that it tried to build a valid token from it and hit a roadblock at the next character.

3. What valid JSON structures start with "n"? #

Only one: the literal null.

To put this in context, JSON only allows these types of values (either as top-level entries or nested inside objects/arrays):

• Objects wrapped in curly braces ({ ... })
• Arrays wrapped in square brackets ([ ... ])
• Strings enclosed in double quotes ("...")
• Numbers (like 42, -3.14, 0)
• Boolean literals (true, false)
• null

Out of all these, null is the only one that starts with the letter "n".

内容的提问来源于stack exchange，提问作者Adelin