from One-off statements to looping statements - methods?

I constantly find myself needing to make a function that needs to do something - ONCE - at the very beginning, and then keep looping through all the rest of it. So my question is - what are possible approaches of programming that?

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you do something once, then proceed to continously looping something else.

    // This code is run AT LEAST once.
} while (someCondition);

Note that this doesn't appear to work in javascript.

Eric5h5s suggestion is:

while (true) 
    // something
    if (!condition) break;