How to get JS script of a Google form?

I owned a google form, how can I get the js script of it?

I click the Script Editor but there is no corresponding js I can find.

I have already searched on internet but no expected answers.

-- update on 20/08/2017

Assume that I owned a form like this : Sample Form.

How can I get the corresponding google script of this form?

i.e.,

function myFunction() {
    // Create a new form, then add a checkbox question, a multiple choice question,
    // a page break, then a date question and a grid of questions.
    var form = FormApp.create('Sample Form');
    var sect1 = form.addSectionHeaderItem();
    var item = form.addCheckboxItem();
    item.setTitle('What condiments would you like on your hot dog?');
    item.setChoices([item.createChoice('Ketchup'), item.createChoice('Mustard'), item.createChoice('Relish')]);
    var item2 = form.addMultipleChoiceItem().setTitle('Do you prefer cats or dogs?');
    //    .setChoiceValues(['Cats','Dogs'])
    //    .showOtherOption(true);
    var sect2 = form.addSectionHeaderItem();
    form.addPageBreakItem().setTitle('Getting to know you');
    form.addDateItem().setTitle('When were you born?');
    var sect3 = form.addSectionHeaderItem();
    var break2 = form.addPageBreakItem().setTitle('Getting to know you 2');

    var choice1 = item2.createChoice('cat', FormApp.PageNavigationType.CONTINUE);
    var choice2 = item2.createChoice('dog', break2);
    item2.setChoices([choice1, choice2]);

    form.addGridItem().setTitle('Rate your interests').setRows(['Cars', 'Computers', 'Celebrities']).setColumns(['Boring', 'So-so', 'Interesting']);
    Logger.log('Published URL: ' + form.getPublishedUrl());
    Logger.log('Editor URL: ' + form.getEditUrl());
}