function randomizeArea(line, col, lines, cols) {
    //
    const randomByte = () => Math.floor(Math.random() * 256)
    //
    // randomize the colour attributes
    for (let l = line; l < (line + lines) && l < LINES; l++)
        for (let c = col; c < (col + cols) && c < COLUMNS; c++)
            displayColours[l * COLUMNS + c] = randomByte()
    //
    // randomize the pixels
    for (let l = line; l < (line + lines) && l < LINES; l++)
        for (let c = col; c < (col + cols) && c < COLUMNS; c++)
            for (b = 0; b < CHARSIZE; b++)
                displayPixels[(l * 8 + b) * COLUMNS + c] = randomByte()
} //                                                               randomizeArea

/** randomizeArea():
 *  Randomizes the specified area of the virtual display.
 *  The area will contain random pixels and colours.
 *
 *  @param [line]   Starting line number, a number from 0 to LINES-1.
 *                  The starting line is at the top of the display.
 *
 *  @param [col]    Starting column number, a number from 0 to COLUMNS-1.
 *                  The starting column is at the left of the display.
 *
 *  @param [lines]  The height of the area to update, from 1 to LINES.
 *                  Any areas out of the display area will be ignored.
 *
 *  @param [cols]   The width of the area to update, from 1 to COLUMNS.
 */
Randomizes the specified area of the virtual display.
The area will contain random pixels and colours.

@param [line]   Starting line number, a number from 0 to LINES-1.
The starting line is at the top of the display.

@param [col]    Starting column number, a number from 0 to COLUMNS-1.
The starting column is at the left of the display.

@param [lines]  The height of the area to update, from 1 to LINES.
Any areas out of the display area will be ignored.

@param [cols]   The width of the area to update, from 1 to COLUMNS.
Randomizes the specified area of the virtual display . The area will contain random pixels and colours . @param [ line ] Starting line number a number from 0 to LINES - 1 . The starting line is at the top of the display . @param [ col ] Starting column number a number from 0 to COLUMNS - 1 . The starting column is at the left of the display . @param [ lines ] The height of the area to update from 1 to LINES . Any areas out of the display area will be ignored . @param [ cols ] The width of the area to update from 1 to COLUMNS .
function randomizeArea(line, col, lines, cols) {
    const randomByte = () => Math.floor(Math.random() * 256)
    for (let l = line; l < (line + lines) && l < LINES; l++)
        for (let c = col; c < (col + cols) && c < COLUMNS; c++)
            displayColours[l * COLUMNS + c] = randomByte()
    for (let l = line; l < (line + lines) && l < LINES; l++)
        for (let c = col; c < (col + cols) && c < COLUMNS; c++)
            for (b = 0; b < CHARSIZE; b++)
                displayPixels[(l * 8 + b) * COLUMNS + c] = randomByte()
} 
function randomizeArea ( line , col , lines , cols ) { const randomByte = ( ) => Math . floor ( Math . random ( ) * 256 ) for ( let l = line ; l < ( line + lines ) && l < LINES ; l ++ ) for ( let c = col ; c < ( col + cols ) && c < COLUMNS ; c ++ ) displayColours [ l * COLUMNS + c ] = randomByte ( ) for ( let l = line ; l < ( line + lines ) && l < LINES ; l ++ ) for ( let c = col ; c < ( col + cols ) && c < COLUMNS ; c ++ ) for ( b = 0 ; b < CHARSIZE ; b ++ ) displayPixels [ ( l * 8 + b ) * COLUMNS + c ] = randomByte ( ) }
randomizeArea():
  Randomizes the specified area of the virtual display.
randomizeArea () : Randomizes the specified area of the virtual display .
//
 //
 // randomize the colour attributes
 //
 // randomize the pixels
 //                                                               randomizeArea
