Code calculated using the remaining words of JavaScript

First look at html Code :

<Textarea name = "Description" onkeyup = "checklength (this);"> </textarea>
<Br/> <small> maximum text length: 250. Remaining: <span id = "chleft"> 250 </span>. </small>
It can be seen that onkeyup is an event triggered when the user leaves the keyboard. The parameter passed is this (that is, the current document area)

Then let's take a look at the JS Code:

<SCRIPT type = "text/JavaScript">
Function checklength (which ){
VaR maxchars = 250;
If (which. value. length> maxchars)
Which. value = which. value. substring (0, maxchars );
VaR curr = maxchars-which. value. length;
Document. getelementbyid ("chleft"). innerhtml = curr. tostring ();
}
</SCRIPT>
In the function, the maxchars variable is specified first (the maximum number of characters available in the input area. Note that this variable is a value that can be used for calculation)

Then, the length of the entered character in textarea is obtained from the parameter and compared with the maximum length specified previously.
When the length of the entered character exceeds the range, substring is used to forcibly limit its length (0, maxchars), which means that the input range is 0 to maxchars.

VaR curr = maxchars-which. value. length; is used to calculate the number of characters available and save the value in curr.

Finally, use getelementbyid to locate the object whose ID is chleft (span in This html), convert the value in curr into a string using the tostring method, and feed it back to the span tag.