是什么 <!— --> 以html表示

Question

So in html you frequently see

<!-- HTML TEXT HERE -->

What is the purpose of Greater than exclamation mark double hyphens and double hyphen less than ?

Answer 1

These are comments , that are not visible to the user but only when you view the actual HTML.

They are also useful in commenting out a block of code when you're doing testing, that way you can prevent from having to cut and paste the code else where, and then copy them back.

Additionally, some developers used them to 'hide' code, usually in scripts, to avoid a chunk of code displayed for browsers that disable Javascript.

<script>
<!--
function displayMsg() {
    alert("Hello World!")
}
//-->
</script> 

That will prevent code from function .... to } from showing up on browsers that have Javascript disabled. You'll also frequently see tags.

It is also used for conditional comments , which are only supported in Internet Explorer, whereby you adapt your HTML to legacy browsers like IE6, so your shiny website doesn't break on old browsers. See here for more info .

Here's an example of conditional comments you might see:

<!--[if lte IE 8]><link rel="stylesheet" href="css/ie/v8.css" /><![endif]-->

That means if Internet Explorer is Version 8 (old and outdated) load that stylesheet.

For more information about comments, this is a good tutorial .

Answer 2

Those are HTML Comments.

Like comments in code, you can use them to describe why you're doing what you're doing in your markup so save the next guy to work on your code a whole lot of headaches.

Answer 3

They are comments.
comments are for describing your code so if other programmers(or even yourself!) want to see what it's used for,it'll make it more easy to understand.
comments are used in all programming languages.in html, comments are <!-- Comments --> but in other languages Comments are //comments... or /* comments...*/ so don't get confused if you see them.
THIS article will show you why we use comments in different programming languages.