Using Regexp match to access array/object

Question

I have:

 window.page="home";
 document.getElementsByTagName("title")[0].innerHTML=
      "hello.com | $page".replace(/\$([^\s]*)/g,window["$1"]);

The idea is to get:

 <title>hello.com | home</title>

But I instead get:

 <title>hello.com | undefined</title>

When I do the following:

 document.getElementsByTagName("title")[0].innerHTML=
      "hello.com | $page".replace(/\$([^\s]*)/g,"$1");

I get:

 <title>hello.com | page</title>

This is because the function is taking "$1" as an argument with which to map its output. I'm wondering if there is a way to use the capture group to access an array/object?

Use a callback, .replace(/\$(\S*)/g, function($0,$1) {return window[$1];}) — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jul 23, 2017 at 21:44

Wiktor Stribiżew · Accepted Answer · 2017-07-23 21:48:07Z

1

You cannot use a backreference that can only be used a part of the string replacement pattern as an argument. You need to use a replace callback for that.

Use

.replace(/\$(\S*)/g, function($0,$1) {return window[$1];})

Note that \S (a non-whitespace) is shorter than [^\s] (not a whitespace).

In function($0,$1), the $0 stands for the whole match, while $1 stands for the Group 1 contents.

answered Jul 23, 2017 at 21:48

Wiktor Stribiżew

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