Sample code for JavaScript to implement textarea to limit the number of input characters

This article mainly introduces the principles and methods of JS to implement textarea to limit the number of input words. It has a very good reference value. Let’s take a look at it with the editor.

Realize textarea to limit the number of input characters (including Chinese, only 10 can be input, and full ASCII code can input 20)

Textarea is called text area, also known as text area, which is a multi-line text input control with scroll bars. It is often used in submission forms on web pages. Unlike the single-line text box text control, it cannot limit the number of words through the maxlength attribute. For this reason, other methods must be found to limit it to meet the preset requirements.

The usual approach is to use #scripting language to limit the number of words entered in the textarea text field, which is simple and practical. Suppose we have a textarea text area with an ID of txta1. We can limit its keyboard input characters to 10 characters (Chinese characters or other small-angle characters) through the following code:

＜script language="#" type="text/ecmascript"＞ 
window.onload = function() 
{ 
document.getElementById('txta1').onkeydown = function() 
{ 
 if(this.value.length >= 10) 
  event.returnValue = false; 
} 
} 
＜/script＞

Its principle is to monitor the text area with the specified ID number through the keydown (keyboard key press) event. As you can imagine, it can only limit keyboard input. If the user pastes the text in the clipboard through the right mouse button Text, it cannot control the word count.

Input via keyboard, only 10 characters can be entered in the above text area. However, our goal was not achieved! Just copy some text and try pasting it with the right mouse button and see what happens.

You can find other JS scripts similar to the above on the Internet. No matter how excellent they are, their principles are the same. They monitor the text area through keyboard key operation events such as keydown, keyup or keypress. Input cannot prevent the right mouse button from being pasted. For this reason, if we must really limit the number of words in the textarea, we have to add another lock to the web page - disabling the right mouse button. This will undoubtedly require additional overhead, and it may also be Web page creators may not be willing to do it. In fact, there is a simpler way, using the onpropertychange attribute.

onpropertychange can be used to judge the value of a predetermined element. When the value of the element changes, the judgment event will be triggered. It only cares about the value of the monitored element, avoiding the source of the input, so that it can It ideally achieves our goal of limiting the number of words. It belongs to the category of JS and can be used nested in the form box area representative. The following is the code and effect style. You can test the input as above, and you will find that it really achieves the purpose: no matter what method is used to input, it can only input 100 Characters (Chinese characters or other small symbols):

Code:

<textarea onpropertychange="if(value.length>100) value=value.substr(0,100)" class="smallArea" cols="60" name="txta" rows="8"></textarea>

Of course, in order to be more secure, the background of processing form data The script program should also check the submitted data again. If the number of words exceeds the preset number, handle it accordingly, so as to achieve the purpose of truly limiting the number of words. (End)

Another way to limit the number of input characters in textarea (including Chinese, only 10 characters can be entered, and full ASCII code can enter 20 characters)

<script> 
function check() { 
var regC = /[^ -~]+/g; 
var regE = /\D+/g; 
var str = t1.value; 
if (regC.test(str)){ 
 t1.value = t1.value.substr(0,10); 
} 
if(regE.test(str)){ 
 t1.value = t1.value.substr(0,20); 
} 
} 
</script> 
<textarea maxlength="10" id="t1" onkeyup="check();"> 
</textarea>

There is another way:

function textCounter(field, maxlimit) { 
if (field.value.length > maxlimit){ 
field.value = field.value.substring(0, maxlimit); 
}else{ 
document.upbook.remLen.value = maxlimit - field.value.length; 
} 
} 
<textarea name=words cols=19 rows=5 class=input1 onPropertyChange= "textCounter(upbook.words, 50) "> textarea>

Number of remaining words:

<input name=remLen type=text id= "remLen " style= "background-color: #D4D0C8; border: 0; color: red " value=50 size=3 maxlength=3 readonly>
function LimitTextArea(field){ 
 maxlimit=200; 
 if (field.value.length > maxlimit) 
  field.value = field.value.substring(0, maxlimit); 
  
 }
<textarea cols=50 rows=10 name="comment" id="commentarea" onKeyDown="LimitTextArea(this)" onKeyUp="LimitTextArea(this)" onkeypress="LimitTextArea(this)" >
</textarea>

title="The textarea width must less than 300 characters." When placed in the textarea, it prompts for the maximum number of bytes.

For example:

<textarea title="The textarea width must less than 300 characters." cols=50 rows=10 name="comment" id="commentarea" onKeyDown="LimitTextArea(this)" 
onKeyUp="LimitTextArea(this)" onkeypress="LimitTextArea(this)" ></textarea>

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