Javascript Spread Operator ...

The javascript spread operator ... is a convenient way to insert an array into a second array.  Used mainly when defining the array data.  Consider the following:

/****
 * The x array is placed inside of noSpread as a child array inside.
 * noSpread array is now ['u', Array(2), 3, 7]
 ****/
let x = ['a', 2];
let noSpread = ['u', x, 3, 7];

/***
 * using the spread operator ...x
 * the spread array is now ['u', 'a', 2, 5, 6]
 ***/ 
let x = ['a', 2];
let spread = ['u', ...x, 5, 6];