replacing a text with "$$$", gives truncated result in Javascript [duplicate]

Question

var text="$$$ $$ $"; 
var dummy="hello world"; 
dummy.replace("world", text);

expected output:

hello $$$ $$ $

actual output:

hello $$ $ $

i don't understand why this is happening. kindly help. it doesn't seem to happen with other symbols though.

thanks

Answer 1

It's because $ has a special meaning in regular expressions, which replace uses.

See this question for more details: link

Answer 2

The short answer is "because that's how String.replace works".

The docs at Mozilla Development Network are helpful here:

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

The replacement string can include the following special replacement patterns:

• $$ Inserts a "$".
• $& Inserts the matched substring.

And so forth.. (there's more replacement rules, but I'm not going to quote the whole MDN page)

So, if we change your sample to:

var text="$$ ($&) $"; 
var dummy="hello world"; 
dummy.replace("world", text);

We get as a result:

"hello $ (world) $"

In short $& (and other sequences like $1 and $'), mean special things, and the way you escape a plain $ is by preceding it with another $.