NullPoiиteя NullPoiиteя - 5 months ago 15
Javascript Question

How to check string length with JavaScript

I want to get the string length when a key is pressed like StackOverflow does.

Example of StackOverflow showing length

I have tried to do this with

onblur
, but it's not working. How do I do this?

Answer

As for the question which event you should use for this: use the input event, and fall back to keyup/keydown in older browsers.

Here’s an example, DOM0-style:

someElement.oninput = function() {
  this.onkeydown = null;
  // Your code goes here
};
someElement.onkeydown = function() {
  // Your code goes here
};

The other question is how to count the number of characters in the string. Depending on your definition of “character”, all answers posted so far are incorrect. The string.length answer is only reliable when you’re certain that only BMP Unicode symbols will be entered. For example, 'a'.length == 1, as you’d expect.

However, for supplementary (non-BMP) symbols, things are a bit different. For example, '

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