Question

how can we click on a button using javascript in selenium and if the button does not have id

Comments

I'm not sure what role JavaScript plays, but I know for certain that there are other Locator techniques that can be used. They are by.name(), by.classname(), by.cssSelector(), by.xpath(), etc. Even if the by.id() is not present, one of these will definately be present. Do let me know if that's the case.

Answer 1

If button does not have id, you can write locator based on other locators strategies. 

For example here i am using xpath locator then you need to click button by using Java Script executor in following way...

JavascriptExecutor js = (JavascriptExecutor) driver;//create instance of javascript executor to do actions

WebElement nextButton = driver.findElement(By.xpath("//span[contains(text(),'Next')]"));

js.executeScript("arguments[0].click();", nextButton);

Answer 2

       WebElement webElement=driver.findElement(By.xpath(element));
        JavascriptExecutor js = (JavascriptExecutor) driver;

        js.executeScript("arguments[0].click();",webElement);