JavaScript Create substring from IndexOf not working

Question

I'm trying to trim the values of an href before and after the domain name using JavaScript. For example, http://www.google.com/about-us should be trimmed to www.google.com.

var str = "http://www.google.com/about-us";
var str_before = str.replace("http://","");
document.write(str_before); // Returns ("www.google.com/about-us")

// Trim everything after the domain name

var link = str_before.substring(0, str_before.indexOf('/'));
document.write(link); // Returns "www.google.com/about-uswww.google.com"

I don't know why this is happening. Any help would be greatly appreciated!

var a = document.createElement("a"); a.href = str; a.host; // "www.google.com" — user1106925
– user1106925, Commented Dec 29, 2016 at 17:23
Nope, it's document.write tricking you. Use console.log to check the results of your code. — Teemu
– Teemu, Commented Dec 29, 2016 at 17:23
do not use document.write, forget it exists. Why do beginner courses teach people to use it, it is not the 90/00s any more. — epascarello
– epascarello, Commented Dec 29, 2016 at 17:26
@epascarello Not only some courses, but even MDN examples often use dw(). I've left feedback for Mozilla a couple of years ago about using dw() in examples, but not sure, if its use has been decreased. — Teemu
– Teemu, Commented Dec 30, 2016 at 12:44

Martin Zikmund · Accepted Answer · 2016-12-29 17:30:08Z

2

You are seeing the output of the previous document.write concatenated with the output of the second document.write. If you add a line break to the output, you will see the real output as two lines and you will see that the result is in fact correct.

Try the code snippet below:

var str = "http://www.google.com/about-us";
var str_before = str.replace("http://","");
document.write(str_before); // Outputs "www.google.com/about-us"

// Trim everything after the domain name
var link = str_before.substring(0, str_before.indexOf('/'));

//add line break to the output
document.write( '<br />' );

//output the resulting link
document.write( link );

edited Dec 29, 2016 at 17:30

answered Dec 29, 2016 at 17:23

Martin Zikmund

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1 Comment

Jeff P. Over a year ago

Thanks! I was overlooking the document.write() line I had in place.

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