How do I replace the very last character in a text area field?

For examples

test1, test2, test3, test4,

How do I replace the very last character (comma) with a peri开发者_如何学Good?

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This removes the trailing comma if any and adds a period:

textarea.value = textarea.value.replace(/,$/, "") + ".";

textarea.value is a string which has a replace method. As first argument, a regular expression is given (characterized by a single leading /) which matches a comma on the end ($). The match (if any) is replaced by nothing (removed) and a period is appended.

Beware that this code resets the scrolling (at least in Firefox) and the cursor position.

Another snippet that removed a traling comma, but which does not add a period if there is no trailing comma:

textarea.value = textarea.value.replace(/,$/, ".");

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You can use .slice() to remove the last character, then just concatenate the period.

var ta = document.getElementById('mytextarea');

ta.value = (ta.value.slice(0,-1) + '.');

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var yourTextarea = document.getElementById('textareaId'); // get your textarea element
var val = yourTextarea.value; // get text, written in textarea
val = val.slice(0,-1); // remove last char
val += charToReplace; // add char, that you want to be placed instead of comma
yourTextarea.value = str; // set just edited text into textarea

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You can check for a comma at the end and then replace it:

if (myString.substr(myString.length - 1, 1) == ',') {
  myString = myString.substr(0, myString.length - 1) + '.';
}

Or you can blindly replace it:

  myString = myString.substr(0, myString.length - 1) + '.';

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document.getElementsByTagName('textarea')[0].innerHTML = document.getElementsByTagName('textarea')[0].innerHTML.substr(0, document.getElementsByTagName('textarea')[0].innerHTML.length - 1)