Calling the builtin methods String.prototype.split and String.prototype.replace with a string as the first argument makes the methods search for that exact string. Providing a regular expression instead of the string makes the methods perform a regular expression search.

Calling the methods with a string that has the format of a regular expression is likely a mistake because the methods will not convert the string to a regular expression.

Call String.prototype.split and String.prototype.replace with a regular expression as the first argument unless you want an exact search.

The following code snippet shows a call to String.prototype.replace. The purpose of the call is to remove all characters that are not alphanumeric.

var cleaned = input.replace("[^a-zA-Z0-9]+", "");

Unfortunately, the first argument is a string and not a regular expression, so the call will only remove the first substring that is exactly "[^a-zA-Z0-9]+".

Instead, the first argument should be a regular expression with the global flag set:

var cleaned = input.replace(/[^a-zA-Z0-9]+/g, "");

Mozilla Developer Network: String.prototype.split

Mozilla Developer Network: String.prototype.replace