JavaScript Strings with Compare signs are Ignored?

Question

I've noticed an issue I've never encountered before. Strings in JavaScript that contain < are ignored. Why is that? Here are a few of the results I've noticed:

msg = "<This entire string would be ignored."
msg = "This part of the string is ok. <While this part is ignored."
msg = "<This part is ignored> But this half of the string will still print."

Is this some kind of special escape character or something? What is it used for? Additionally, what would be a work around for this?

Here is code:

var msg = "This is my message <This is ignored";
document.write(msg);

I don't see the character is getting escaped. Tried in chrome developer console. — Vimalraj Selvam
– Vimalraj Selvam, Commented Oct 14, 2017 at 7:32
You set the innerHTML of an element with that string, right? Don't do that. You want to set the textContent. — Tomalak
– Tomalak, Commented Oct 14, 2017 at 7:36
< is used to indicate HTML tags, like <div>, <a>, etc. — Barmar
– Barmar, Commented Oct 14, 2017 at 7:40
Gotcha, Thanks. I wouldnt think it would do that when contained inside a string? — Brendan
– Brendan, Commented Oct 14, 2017 at 7:42

Aanand Kainth · Accepted Answer · 2017-10-14 07:40:17Z

2

This is not an issue with JavaScript; it's an issue with your code. Here's the problem, as suggested by @Tomalak.

You are using innerHTML as opposed to textContent, which will try to parse the string as a tag with attributes, for example.

<This part is ignored> → <this> with the part, is, and ignored attributes

answered Oct 14, 2017 at 7:40

Aanand Kainth

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1 Comment

Aanand Kainth Over a year ago

It appears that you had a question about it not happening in a string. JavaScript interprets the string, as a string; when you set the innerHTML the browser converts it to HTML, but it is still a string in your code. For example: var msg = '<brendan>'; document.body.innerHTML = msg; console.log(msg);

Barmar · Accepted Answer · 2017-10-14 07:47:15Z

When you write something with document.write(), it's simply inserted into the HTML source of the page at that location. As a result, if there are any HTML tags in it, they will be parsed. Anything that begins with < is treated as an HTML tag. If you want to write a literal <, use <:

var msg = "This is my message &lt;This is NOT ignored";
document.write(msg);

You really shouldn't use document.write() in the first place, that's 1990's Javascript; assign to innerHTML or textContent of an element. innerHTML will be parsed as HTML, textContent will be treated as literal text and not parsed.

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