创建一个正则表达式来替换字符串中最后一次出现的字符

Question

I need to create a regex which should look for the last '*' irrespective of the whitespace in the string. Then, I need to replace that string with some text.

Currently, it is replacing the first occurence of '*' in the string.

How do I fix it?

Here's my code:

const regex = /\*/m;
const str = 'Field Name* * ';
const replaceStr = ' mandatory';
const result = str.replace(regex, replaceStr);
console.log('Substitution result: ', result);

Here, the output should be 'Field Name* mandatory'. But what I get is 'Field Name mandatory *'.

Answer 1

Instead of RegEx, use String#substring and String.lastIndexOf as below

 const str = 'Field Name* * '; const replaceStr = 'mandatory'; const lastIndex = str.lastIndexOf('*'); const result = str.substring(0, lastIndex) + replaceStr + str.substring(lastIndex + 1); console.log('Substitution result: ', result);

Still want to use RegEx?

 const regex = /\*([^*]*)$/; const str = 'Field Name* * Hello World;'; const replaceStr = ' mandatory'. const result = str,replace(regex, (m; $1) => replaceStr + $1). console:log('Substitution result, '; result);

Answer 2

Short regex magic (shown on extended input str ):

 const regex = /\*(?=[^*]*$)/m, str = 'Field Name* * * * ', replaceStr = ' mandatory', result = str.replace(regex, replaceStr); console.log('Substitution result: ', result);

• (?=[^*]*$) - lookahead positive assertion, ensures that the former \* is matched only if it's followed by [^*]* (non-asterisk char right up to the end of the string $ )

Answer 3

Just let .* consume before last * and capture it. Replace with captured $1 mandatory .

 let str = 'Field Name* * '; let res = str.replace(/(.*)\*/,'$1mandatory'); console.log(res);

See this demo at regex101

• If you have Field Name* *abc and want to strip out end as well, use (.*)\*.*
• If you have multline input, use [\S\s]* instead of .* to skip over newlines