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Trying to print a unicode code point table

I am trying to make a unicode code points table that prints the code points till U+300
I change the number into hexadecimal and concatenate it with the unicode escape sequence.
When I try to concatenate the hexadecimal number with '\u' I get an error SyntaxError: Invalid Unicode Escape Sequence
Here's the code
How can I fix that error?

Change the print statement to print(num + ' => ' + String.fromCharCode("0x" + num));

Instead of this:
print(num + ' => ' + '\u' + num);
use this:
print(num + ' => ' + '\\u' + num);
Or, more concisely,
print(num + ' => \\u' + num);
You need to escape the \ itself to include it in a string literal.

String with both ' & "

I have an HTML element like this
<div id='test' onclick='window.location="http://example.com/";'></div>
I'm annoyed because I would like to put this into a string but I'm not able since this element use both ' and " in its syntax.
How can I store such syntax into a string?

Try This:
var data = "<div id='test' onclick='window.location=\"http://example.com/\";'></div>"
alert(data)

Just escape the strings with a \.
var myString = "<div id='test' onclick='window.location=\"http://example.com/\";'></div>";

escape the ' or " with a backslash
var testString = '<div id=\'test\' onclick=\'window.location=\"http://example.com/\";\'></div>';
alert(testString);

you can use backslash \ for putting special character in string
for example for storing string "(double quotes) and '(single quotes) you can write
var s="\"\'"

What's wrong with my regex replace functions?

var storeName = "St. Bob's Store";
var storeId = storeName.replace(/./g,"").replace(/\s/g, '').replace(/'/g,"")
$('#storeName').html(storeName)
$('#storeId').html("(" + storeId + ")")
console.log("Updating " + storeName + "(" + storeId + ")");
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="storeName">Loading</div>
<div id="storeId">loading</div>
What am I doing wrong with storeId? It's empty.

If you want to match "dot" char, you have to escape it, like this:
var storeId = storeName.replace(/\./g,"").replace(/\s/g, '').replace(/'/g,"");
Here's a fiddle: https://jsfiddle.net/e63bq01L/
If not escaped, the dot matches all characters in a string.

You have to escape the dot character:
storeName.replace(/\./g,"").replace(/\s/g, '').replace(/'/g,"")
Otherwise, you will replace everything.

Transform all escaped chars to its original value

My backend has json string arrays, but some of the chars are escaped when send the value to frontend, like " é. How can I change all of the escaped chars to its original value? For some reason, I can't use other JS frameworks. The innerHTML seems didn't be supported in all browsers(like firefox).

You can use below snippet to unescape the string
//Snippet#1
var str="é";
var str_esc=escape(str);
document.write("Escaped String: " + str_esc + "<br>")
document.write("Original String: " + unescape(str_esc))
or
//Snippet#2
var str="é";
var enc_str = encodeURI(str);
var dec_str = decodeURI(enc_str);
document.write("Escaped String: " + enc_str + "<br>")
document.write("Original String: " + dec_str)

Why does this regex/DOM character entity tester return `undefined`?

var str = 'let us pretend that this is a blog about gardening&cooking; here's an apostrophe & ampersand just for fun.';
This is the string I'm operating on. The desired end result is: "let us pretend that this is a blog about gardening&cooking; here's an apostrophe & ampersand just for fun."
console.log('Before: ' + str);
str = str.replace(/&(?:#x?)?[0-9a-z]+;?/gi, function(m){
var d = document.createElement('div');
console.log(m);
d.innerHTML = m.replace(/&/, '&');
console.log(d.innerHTML + '|' + d.textContent);
return !!d.textContent.match(m.replace(/&/, '&')[0]) ? m : d.textContent;
});
console.log('After: ' + str);

The problem is that HTML doesn't support XML's '
To avoid the issue you should use ' instead of '
For more information look at this post:
Why shouldn't ' be used to escape single quotes?

This should do what you want:
str.replace(/&([#x]\d+;|[a-z]+;)/g, "&$1")
or, with a positive lookahead:
str.replace(/&(?=[#x]\d+;|[a-z]+;)/g, "&")
I don't think you need any HTML2text en-/decoding.