Javascript replace first letter of every string?

Question

I am trying to make a script that should replace strings. This is what my current replace function does:

let message2 = message1.replace(/hello/g, "[size=medium]h[/size]ello");

As you can see, this adds the size=medium tag to the h of the word. This works good, but I want this to work in every possible capitalization and still remain in that capitalization.

For example: "hELLo" should be replaced with "[size=medium]h[/size]ELLo"

and

"HELLo" be replaced with "[size=medium]H[/size]ELLo"

Only the h/H should be wrapped in the tag, but I am not sure how to perform something like this. Big thanks for any input on this!

You mean "HELLo" be replaced with "[size=medium]H[/size]ELLo"? — Cuong Le Ngoc
– Cuong Le Ngoc, Commented Jul 14, 2019 at 2:01
Yes you are correct. Sorry i realized this just now as well @CuongLeNgoc — javgogel
– javgogel, Commented Jul 14, 2019 at 2:01
Are you looking to do this only for the word "hello" and any variations of it, or do you mean to do this for every word? Also can you clarify what you mean by "word"? — smac89
– smac89, Commented Jul 14, 2019 at 2:15

melpomene · Accepted Answer · 2019-07-14 02:04:50Z

2

You can use capture groups:

message1.replace(/(h)(ello)/ig, "[size=medium]$1[/size]$2")

Or alternatively, look-ahead:

message1.replace(/h(?=ello)/ig, "[size=medium]$&[/size]")

answered Jul 14, 2019 at 2:04

melpomene

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3 Comments

Cuong Le Ngoc Over a year ago

In case of message1 = "ahello", it still replace the h letter.

Cuong Le Ngoc Over a year ago

But the question is replace the first letter.

melpomene Over a year ago

@CuongLeNgoc h is the first letter of the string hello.

Cuong Le Ngoc · Accepted Answer · 2019-07-14 02:31:37Z

1

You can try this regex:

var a = 'hello';
var b = 'HEllo';

console.log(a.replace(/^h/i, "[size=medium]$&[/size]"))
console.log(b.replace(/^h/i, "[size=medium]$&[/size]"))

Of if you just want to replace h in hello, you can use look ahead:

var a = 'HEllo';
var b = 'Halo';

console.log(a.replace(/^h(?=ello)/i, "[size=medium]$&[/size]"))
console.log(b.replace(/^h(?=ello)/i, "[size=medium]$&[/size]"))

edited Jul 14, 2019 at 2:31

answered Jul 14, 2019 at 2:03

Cuong Le Ngoc

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1 Comment

CertainPerformance Over a year ago

Because the capture group is the full match, you can use $& instead (and remove the capture group entirely). If it's desired to only replace hs which end in ello you can lookahead for the ello

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