Interfaces DOM, created to control web pages, are not a part of standard ECMAScript or JavaScript is direct. Officially, they are defined by separate effort on standardization W3C; practically, browser performance differs from standards and from each other, and not all browsers fulfil JavaScript.

To deal with these distinctions, authors JavaScript can try to write obedient to standards the code which also will be fulfilled correctly by the majority of browsers; bringing it, they can write the code which checks on presence of a certain browser, shows and behaves in another way if they are not accessible. In some cases, two browsers can and carry out feature, but with various behaviour, and authors can find practical to detect what the browser controls, and to change behaviour of their original to correspond. Programmers can use also libraries or toolings which take into consideration distinctions of a browser.



Besides, originals will not work on all users. For example, the user can:

To use an old or rare browser with incomplete or unusual support DOM,

To use PDA or a browser of a mobile phone which cannot fulfil JavaScript,
Or visually or otherwise has hurt and used a speech browser.



To support these users, authors of a network can try to create pages which (browsers) which do not support JavaScript page worsen gracefully on user's agents.