How to write a regex expression to check a valid XML element NCName in javascript?

NCName means that it must start with a letter or underscore, and can only contain letters, digits, underscores, hyphens, and periods.I have try to write the regex like this,but I think it may be wrong.

if(/^([_]|[a-zA-Z]+[\w\W])$/.test('abc' ))  console.log('match')

Your ^([_]|[a-zA-Z]+[\w\W])$ pattern matches a string that is either equal to _ ([_]) or (|) is formed of 1+ letters ([a-zA-Z]+) followed with any char ([\w\W]). So, it cannot validate the strings of the type you mention.

You may use

/^[a-zA-Z_][\w.-]*$/

See the regex demo and the graph (source) below:

Details

• ^ - start of string
• [a-zA-Z_] - a letter or _
• [\w.-]* - 0 or more letters, digits, underscores, dots or hyphens
• $ - end of string