Selenium: Can I set any of the attribute value of a WebElement in Selenium?

I have a WebElement, I want to reset its an attribute's value to some other value (for e.g. attr is the attribute, and I want to change its original value=1 to new value=10).

Is it possible? I am using Selenium 2.0 (WebDriver.)

You would have to use the JavascriptExecutor class:

WebDriver driver; // Assigned elsewhere
JavascriptExecutor js = (JavascriptExecutor) driver;
js.executeScript("document.getElementById('//id of element').setAttribute('attr', '10')");

If you're using the PageFactory pattern or already have a reference to your WebElement, then you probably want to set the attribute, using your existing reference to the WebElement. (Rather than doing a document.getElementById(...) in your javascript)

The following sample allows you to set the attribute, using your existing WebElement reference.

Code Snippet

import org.openqa.selenium.WebElement;
import org.openqa.selenium.remote.RemoteWebDriver;
import org.openqa.selenium.support.FindBy;

public class QuickTest {

    RemoteWebDriver driver;

    @FindBy(id = "foo")
    private WebElement username;

    public void exampleUsage(RemoteWebDriver driver) {
        setAttribute(username, "attr", "10");
        setAttribute(username, "value", "bar");
    }

    public void setAttribute(WebElement element, String attName, String attValue) {
        driver.executeScript("arguments[0].setAttribute(arguments[1], arguments[2]);", 
                element, attName, attValue);
    }
}

Fancy C# extension method based on previous answers:

public static IWebElement SetAttribute(this IWebElement element, string name, string value)
{
    var driver = ((IWrapsDriver)element).WrappedDriver;
    var jsExecutor = (IJavaScriptExecutor)driver;
    jsExecutor.ExecuteScript("arguments[0].setAttribute(arguments[1], arguments[2]);", element, name, value);

    return element;
}

Usage:

driver.FindElement(By.Id("some_option")).SetAttribute("selected", "selected");

Another to answer this question available here answered by @nilesh https://stackoverflow.com/a/19934852/2079692

public void setAttributeValue(WebElement elem, String value){
    JavascriptExecutor js = (JavascriptExecutor) driver;
    js.executeScript("arguments[0].setAttribute(arguments[1],arguments[2])",
        elem, "value", value
    );
}

this takes advantage of selenium findElementBy function where xpath can be used also.