Tricky Javascript regex replace

Question

I'm coding a custom markdown parser that should preprocess user input so that each line of the input that starts with three ticks should have the reference code trimmed and all it's spaces replaced with underscores. So in this fiddle

var e = document.getElementById("thetext");
var feedback = document.getElementById("feedback");

var sorted = function(haystack) {
  var re = /$```\s*(\S+)(\s+)(\S+)\s*$/g;
  return haystack.replace(re, '```$1_$3');
};

e.addEventListener("blur", function(event) {
  feedback.innerHTML = sorted(e.value);
}, true);

textarea { width: 400px; height: 400px;}

<textarea id="thetext">
A custom block code marker with reference:

``` John 3:16
For God so loved the world 
``` 

another one with two spaces to be replaced:

```1 Cor 2:15-45 
Some other marked up text followed by white space 
```

</textarea>
<pre id="feedback">Tab out to see result</pre>

the output should be exactly like the input except for these two lines:

```John_3:16

and

```1_Cor_2:15-45

Tomalak · Accepted Answer · 2016-06-28 13:53:02Z

3

Tricky replacements are done easiest with a callback function.

var thetext = document.getElementById("thetext");
var feedback = document.getElementById("feedback");

var sorted = function(haystack) {
  var re = /^```(.*)/gm;
  return haystack.replace(re, function ($0, $1) {
      return '```' + $1.trim().replace(/\s/g, '_');
  });
};

thetext.addEventListener("blur", function(event) {
  feedback.textContent = sorted(this.value);
});

textarea { width: 400px; height: 400px;}

<textarea id="thetext">
A custom block code marker with reference:

``` John 3:16
For God so loved the world 
``` 

another one with two spaces to be replaced:

```1 Cor 2:15-45 
Some other marked up text followed by white space 
```

</textarea>
<pre id="feedback">Tab out to see result</pre>

edited Jun 28, 2016 at 13:53

answered Jun 28, 2016 at 13:42

Tomalak

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3 Comments

Tushar Over a year ago

$1.replace(/^\s+|\s+$/g, '').replace(/\s/g, '_') ==> $1.trim().replace(/\s+/g, '_');

Tomalak Over a year ago

@Tushar Nice. Apparently I'm too old-school for that.

Jannie Theunissen Over a year ago

Wow! didn't know you can use a callback. Thanks for the great introduction.

Vladu Ionut · Accepted Answer · 2016-06-28 13:40:44Z

2

Your regex should be multiline . The ^ and $ anchors now match at the beginning/end of each line respectively, instead of beginning/end of the entire string.

/^```\s*(\S+)(\s+)(\S+)\s*$/gm;

answered Jun 28, 2016 at 13:40

Vladu Ionut

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