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...

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...

• javascript
• jquery

• I could be wrong but i think its checking the value and if nothing appears before the "." than it fills it in with a prefix – Drewdin Commented Dec 15, 2011 at 16:52
• This should help you understand what the code does: jsfiddle/fuAwb – Ivan Commented Dec 15, 2011 at 16:54

6 Answers 6

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"

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

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

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

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

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

It simply is replacing the value *. by prefix.

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

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