如何使用JavaScript重建字符串

Question

This code below is now working. Credit to Matt-SL who pointed out the difference between substr and substring

This function serve to add tags to the text in a textarea just like the one you use to put your text in bold in your question&answer on Stackoverflow.

 var lastFocus; $("#bold").click(function (e) { e.preventDefault(); e.stopPropagation(); befString = "<b>"; aftString = "</b>"; dif = aftString.length - befString.length; if (lastFocus) { setTimeout(function () { lastFocus.focus() }, 10); var textEdit = document.getElementById('textEdit'); var befSel = textEdit.value.substr(0, textEdit.selectionStart); var aftSel = textEdit.value.substr(textEdit.selectionEnd, textEdit.length); var select = textEdit.value.substr(textEdit.selectionStart, textEdit.selectionEnd-aftString.length ); textEdit.value = befSel + befString + select + aftString + aftSel; } return (false); }); $("#textEdit").blur(function() { lastFocus = this; }); 

 #textEdit{ width:300px; height:200px; } #bold{ font-size:25px; cursor:pointer; } 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script> <div id="editToolBar" class="editToolBar"> Select all 2's and <span id="bold"></b>click here</b></span> </div> <textarea id="textEdit" type="text" name="textEdit" size="" class="editDocInput" data-type="" >111112222233333</textarea> 

My problem:

I can't figure out why the string is not being put back together properly. Try it and see for you self.

Answer 1

Change the line in which you define var select to use substring() instead of substr() , and no longer subtract aftString.length from textEdit.selectionEnd . This means the text selection indices line up with the expected parameters of the substring() function.

Here is a JSFiddle to demonstrate.

var select = textEdit.value.substring(textEdit.selectionStart, textEdit.selectionEnd);

As per the documentation for selectionEnd , it is the index of the first character after the selection.

The difference between substr and substring is what they expect as their second parameter:

• substr(startIndex, length)
• substring(startIndex, endIndex)