What does string.indexOf(“*.”) do in Javascript?

Question

I'm debugging some code and have found the following code snippet and just don't get what it does:

function appendModelPrefix(value, prefix) {
    if (value.indexOf("*.") === 0) {
        value = value.replace("*.", prefix);
    }
    return value;
}

What does my value string has to look like to get validated by the if-condition? And to what does "*." exactly do? I don't get the wildcard...

Answer 1

I doesn't wildcard. It searches for and then replaces a literal "*." by prefix

indexOf finds the first occurence of "*." in the string:

>>>"aaa*.".indexOf("*.")
3

So your consition will succeed if the string starts with a "*." (index 0)

>>> "*.aaa".indexOf("*.")
0

The replace method will then replace this first occurence of "*." with the chosen prefix

>>> "*.*.".replace("*.", "z")
"z*."

---

BTW, you only get wildcard replacements if you use regexes instead of string patterns:

>>> 'abbbc'.replace(/b+/, 'z')
"azc"

Answer 2

indexOf will give the position of the text inside the string.

So the if statement reads if value starts with "*." then replace it with prefix

Answer 3

If the string starts with the substring *. , then replace it with prefix .

>>> "*.".indexOf('*.')
0
>>> "a*.".indexOf('*.')
1

Answer 4

If your value starts with *. , then it replaces the *. by the prefix parameter.

Answer 5

There is no wilcard-thing in javascript .indexOf() .

It simply is replacing the value *. by prefix .

Answer 6

Its a vanilla string match, if value begins with *. then the *. is replaced by the string in prefix

"aaa" -> "aaa"
"*.a" -> "a" + prefix