var kar = document.getElementByClassName('kar'); kar.style.width="25%";
<!DOCTYPE html> <html> <head> <meta charset=utf-8 /> <title>test</title> <style> .kar { border: 1px solid; margin: 1em; } </style> </head> <body> <button class="btn1">Изменить ширину</button> <div class="kar">Hello World</div> <div class="kar">Hello World</div> <div class="kar">Hello World</div> <div class="kar">Hello World</div> <script> var btn = document.getElementsByClassName('btn1')[0]; btn.onclick = function () { var kar = document.getElementsByClassName('kar'); for (var i = 0; i < kar.length; i += 1) { kar[i].style.width = "25%"; } } </script> </body> </html>
