String Replace in Javascript

I'm very used to ruby's gsub(pattern, replacement) that does a [g]lobal [sub]stitution on a string - that is, it replaces all occurrences of the pattern in the string. If you wanted to just replace the first occurrence of the pattern you could use sub, but I so rarely need to do that I forgot it existed.

Javascript's equivalent, replace, handles things a little bit differently. So much so I was surprised by it's behavior.

replace(pattern, replacement)

pattern can be a string or a RegExp, but you get different replacement behavior depending on which you use.

• If pattern is a string, only the first occurrence of pattern will be replaced.
• If pattern is a RegExp, by default it will replace the first occurrence, unless you pass the global flag to the pattern. So if I wanted to replace asdf in with hjkl in a string, replace(/asdf/, "hjkl") will replace just the first occurrence. To replace all occurrences, it needs to be replace(/adsf/g, "hjkl) (note the global g flag in the regex).

So maybe the moral of the story is to always use a regex (and remember your flags!).

Docs: String.prototype.replace() - JavaScript | MDN