b-rucel

function random_number_increment( min, max, inc ) {
    let min = min || 0;
    let inc = inc || 1;

    if ( !max ) {
        return new Error( 'Need to define max' );
    }

    return Math.floor( Math.random() * ( max - min ) / inc ) * inc + min;
}

b-rucel

<textarea id="text_field_to_save">Everything from here will be saved</textarea>
<input type="text" id="filename_to_save_as" value="filename.txt" />

<script>
function save_text_as_file () {
    let text_to_save = document.getElementById( 'text_field_to_save' ).value;
    let text_to_save_as_blob = new Blob( [ text_to_save ], {
        type: "text/plain"
    } );