How can I convert #FF00 to red(#FF0000)? #190

No, because that doesn't make any sense. #FF00 equates to #FFFF0000 (alpha of 0) as per the CSS specification. I think you're misunderstanding how hex color shorthand works 😉

Shorthand for red is #F00.

var worldString = 'Hello, world';

console.log(worldString.fontcolor('red') +  ' is red in this line');
// '<font color="red">Hello, world</font> is red in this line'

console.log(worldString.fontcolor('FF00') + ' is red in hexadecimal in this line');
// '<font color="FF00">Hello, world</font> is red in hexadecimal in this line'

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/fontcolor#Using_fontcolor

@Qix- But why is FF00 here in red?

That is the <font> tag that hasn't been used in decades. Its color semantics are not governed by CSS. What are you trying to do? Don't use the font tag...

I'm parsing a old website which has a lot of font tag...