How to change word to be uppercase in string and keep the rest?

Question

How to change word to be uppercase in string?

for example I have this string: \u001b[31merror\u001b[39m and if the error word is exist then I want to make her uppercase, so the output should be: \u001b[31mERROR\u001b[39m.

Why when I use regex it will not work? \u001b[31merror\u001b[39m.replace( /(error)/, "$1".toUpperCase())

error can be any lowercase word

score 1 · Accepted Answer · edited Aug 22 '19 at 11:35

It doesn't work because the toUpperCase() is applied at the string "$1" and then the result of that operation i passed as second argument of the replace method; you instead expect that toUpperCase is called with the value found. To do so, you need to pass a function as second argument of replace:

"\u001b[31merror\u001b[39m".replace(/(error)/, $1 => $1.toUpperCase())

That would work (notice, $1 here is just an arbitrary variable name, you can call it as you want).

However, since you said that error is just an example, you could either list all the possible values:

mystring.replace(/(error|info|warning)/, $1 => $1.toUpperCase())

Or just replace everything is between \u001b[31m and \u001b[39m (assuming they don't change):

const mystring = `\u001b[31merror\u001b[39m`;
console.log(
  mystring.replace(/\u001b\[31m(.*)\u001b\[39m/, $1 => $1.toUpperCase())
);

Hope it helps.

YES! Thanks for the explanation and solution! – Jon Sud Aug 22 '19 at 11:30 — Jon Sud, Aug 22 '19 at 11:30

Faisal Rashid · Answer 2 · 2019-08-22T11:17:42.687

-1

Use this

'\u001b[31merror\u001b[39m'.replace(/(error)/, RegExp.$1.toUpperCase())

This will replace the string 'error' and change it to 'ERROR'

edited Aug 22 '19 at 11:17

answered Aug 22 '19 at 11:14

Faisal Rashid

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Thanks but the word can be anything like error, info … the error is just example – Jon Sud Aug 22 '19 at 11:15
I have updated the answer. – Faisal Rashid Aug 22 '19 at 11:18
It is not replacing any lowercase word as is requested but ONLY error – mplungjan Aug 22 '19 at 11:25
@mplungjan The user has asked that he wants to replace a particular lowercase word. He will have to specify the word that he wants to replace as the string may contain more than one lowercase words. – Faisal Rashid Aug 22 '19 at 11:32
_Thanks but the word can be anything like error, info … the error is just example_ – mplungjan Aug 22 '19 at 11:34

How to change word to be uppercase in string and keep the rest?

2 Answers2