with (object)
    statement 

This statement effectively adds object to the front of the scope chain, executes statement, and then restores the scope chain to its original state.

In practice, you can use the with statement to save yourself a lot of typing. In client-side JavaScript, for example, it is common to work with deeply nested object hierarchies. For instance, you may have to type expressions like this one to access elements of an HTML form:

frames[1].document.forms[0].address.value 

If you need to access this form a number of times, you can use the with statement to add the form to the scope chain:

with(frames[1].document.forms[0]) {
    // Access form elements directly here. For example:
    name.value = "";
    address.value = "";
    email.value = "";
} 

This reduces the amount of typing you have to do -- you no longer need to prefix each form property name with frames[1].document.forms[0]. That object is temporarily part of the scope chain and is automatically searched when JavaScript needs to resolve an identifier like address.

Note that there are other, perfectly legitimate ways to save yourself typing. For instance, we could rewrite the previous example as follows:

var form = frames[1].document.forms[0];
form.name.value = "";
form.address.value = "";
form.email.value = ""; 

6.17. try/catch/finally		6.19. The Empty Statement